Glossary of Information Security Terms

Access Control
Access control ensures that resources are only granted to those users who are entitled to them.

Access Control List (ACL)
A mechanism that implements access control for a system resource by listing the identities of
the system entities that are permitted to access the resource.

Account Harvesting
Account harvesting is the process attackers use of collecting all the legitimate account names
on a system.

Advanced Encryption Standard (AES)
An encryption standard developed by NIST and intended to specify an unclassified, publicly
disclosed, symmetric encryption algorithm.

Algorithm
A finite set of step-by-step instructions for a problem-solving or computation procedure,
especially one that can be implemented by a computer.

Asymmetric Cryptography
Public-key cryptography; A modern branch of cryptography in which the algorithms employ a
pair of keys (a public key and a private key) and use different components of the pair for
different steps of the algorithm.

Auditing
Auditing is the information gathering and analysis of assets to ensure such things as policy
compliance and security from vulnerabilities.

Authentication
Authentication is the process of confirming the correctness of the claimed identity.

Authorization
Authorization is the approval, permission, or empowerment for someone or something to do
something within an information system.

Availability
Availability is the need to ensure that the business purpose of the system can be met and that it
is accessible to those who need to use it.

Backdoor
A backdoor is a tool installed after a compromise to give an attacker easier access to the
compromised system around any security mechanisms that are in place.

Bandwidth
Commonly used to mean the capacity of a communication channel to pass data through the
channel in a given amount of time. Usually expressed in bits per second.

Biometrics
Biometrics use physical characteristics of the users, such as palm print, or retina scan to
determine access.

Botnet
A botnet is a large number of compromised computers that are used to create and send spam
or viruses or flood a network with messages as a denial of service attack.

British Standard 7799
A standard code of practice and provides guidance on how to secure an information system. It
includes the management framework, objectives, and control requirements for information
security management systems.

Brute Force
A cryptanalysis technique or other kind of attack method involving an exhaustive procedure that
tries all possibilities, one-by-one; Primarily used in password cracking programs.

Buffer Overflow
A buffer overflow occurs when a program or process tries to store more data in a buffer
(temporary data storage area) than it was intended to hold. Since buffers are created to contain a finite amount of data, the extra information – which has to go somewhere – can overflow into adjacent buffers, corrupting or overwriting the valid data held in them.

Backdoor
A backdoor is a tool installed after a compromise to give an attacker easier access to the
compromised system around any security mechanisms that are in place.

Bandwidth
Commonly used to mean the capacity of a communication channel to pass data through the
channel in a given amount of time. Usually expressed in bits per second.

Biometrics
Biometrics use physical characteristics of the users, such as palm print, or retina scan to
determine access.

Botnet
A botnet is a large number of compromised computers that are used to create and send spam
or viruses or flood a network with messages as a denial of service attack.

British Standard 7799
A standard code of practice and provides guidance on how to secure an information system. It
includes the management framework, objectives, and control requirements for information
security management systems.

Brute Force
A cryptanalysis technique or other kind of attack method involving an exhaustive procedure that
tries all possibilities, one-by-one; Primarily used in password cracking programs.

Buffer Overflow
A buffer overflow occurs when a program or process tries to store more data in a buffer
(temporary data storage area) than it was intended to hold. Since buffers are created to contain
a finite amount of data, the extra information – which has to go somewhere – can overflow into
adjacent buffers, corrupting or overwriting the valid data held in them.

Business Continuity Plan (BCP)
A Business Continuity Plan is the plan for emergency response, backup operations, and postdisaster
recovery steps that will ensure the availability of critical resources and facilitate the
continuity of operations in an emergency situation.

Business Impact Analysis (BIA)
A Business Impact Analysis determines what levels of disruptive impact to a system are
tolerable.

Byte
A fundamental unit of computer storage; the smallest addressable unit in a computer’s
architecture. Usually holds one character of information and usually means eight bits.

Cache Poisoning
Malicious or misleading data from a remote name server is saved [cached] by another name
server. Typically used with DNS cache poisoning attacks.

Certificate-Based Authentication
Certificate-Based Authentication is the use of SSL and certificates to authenticate and encrypt
HTTP traffic.

Chain of Custoday
Chain of Custody is the important application of the Federal rules of evidence and its handling,
and an important part of cyber crime forensics investigations.

Challenge-Handshake Authentication Protocol (CHAP)
The Challenge-Handshake Authentication Protocol uses a challenge/response authentication
mechanism where the response varies every challenge to prevent replay attacks.

Checksum
A value that is computed by a function that is dependent on the contents of a data object and is
stored or transmitted together with the object, for the purpose of detecting changes in the data.

Cipher
A cryptographic algorithm for encryption and decryption.

Ciphertext
Ciphertext is the encrypted form of the message being sent.

Client
A system entity that requests and uses a service provided by another system entity, called a
“server.” In some cases, the server may itself be a client of some other server. A client can be
an endpoint computer such as a laptop, desktop, or mobile computing device such as tablets,
and smartphones.

Cold Site (Disaster Recovery Site)
Cold site. Hardware is ordered, shipped and installed, and software is loaded. Basic
telecommunications, telephone and utility connectivity might need turning on to continue some,
but not all primary site operations. Relocation occurs within weeks or longer, depending on
hardware arrival time, following a disaster. No data synchronization occurs between the primary
and cold site, and could result in significant data loss. Offsite data backup tapes must be
obtained and delivered to the cold site to restore operations. A cold site is the least expensive
option, verses a warm or hot site scenario.

Computer Emergency Response Team (CERT)
An organization that studies computer and network INFOSEC in order to provide incident
response services to victims of attacks, publish alerts concerning vulnerabilities and threats, and
offer other information to help improve computer and network security.

Confidentiality
Confidentiality is the need to ensure that information is disclosed only to those who are
authorized to view it.

Configuration Management
Establish a known baseline condition and manage it; Usually refers to servers, network gear,
and computing endpoints in an enterprise network environment.

Corruption
A threat action that undesirably alters system operation by adversely modifying system
functions or data.

Cost Benefit Analysis
A cost benefit analysis compares the cost of implementing countermeasures with the value of
the reduced risk.

Countermeasure
Reactive methods used to prevent an exploit from successfully occurring once a threat has
been detected. Intrusion Prevention Systems (IPS) commonly employ countermeasures to
prevent intruders form gaining further access to a computer network. Other counter measures
are patches, access control lists and malware filters.

Cover Channels
Covert Channels are the means by which information can be communicated between two
parties in a covert fashion using normal system operations. For example by changing the
amount of hard drive space that is available on a file server can be used to communicate
information.

Cron
Cron is a Unix application that runs jobs for users and administrators at scheduled times of the
day.

Cryptanalysis
The mathematical science that deals with analysis of a cryptographic system in order to gain
knowledge needed to break or circumvent the protection that the system is designed to provide.
In other words, convert the cipher text to plaintext without knowing the key.

Cryptographic Algorithm or Hash
An algorithm that employs the science of cryptography, including encryption algorithms,
cryptographic hash algorithms, digital signature algorithms, and key agreement algorithms.

Data Custodian
A Data Custodian is the entity currently using or manipulating the data, and therefore,
temporarily taking responsibility for the data.

Data Encryption Standard (DES)
Availability is the need to ensure that the business purpose of the system can be met and that it
is accessible A widely-used method of data encryption using a private (secret) key. There are
72,000,000,000,000,000 (72 quadrillion) or more possible encryption keys that can be used. For
each given message, the key is chosen at random from among this enormous number of keys.
Like other private key cryptographic methods, both the sender and the receiver must know and
use the same private key.

Data Owner
A Data Owner is the entity having responsibility and authority for the data.
Day Zero Attack
The “Day Zero” or “Zero Day” is the day a new vulnerability is made known. In some cases, a
“zero day” exploit is referred to an exploit for which no patch is available yet. (“day one”-> day at
which the patch is made available).

Decryption
Decryption is the process of transforming an encrypted message into its original plaintext.

Defacement
Defacement is the method of modifying the content of a website in such a way that it becomes
“vandalized” or embarrassing to the website owner.

Defense In-Depth
Defense In-Depth is the approach of using multiple layers of security to guard against failure of
a single security component.

Demilitarized Zone (DMZ)
In computer security, in general a demilitarized zone (DMZ) or perimeter network is a network
area (a subnetwork) that sits between an organization’s internal network and an external
network, usually the Internet. DMZ’s help to enable the layered security model in that they
provide subnetwork segmentation based on security requirements or policy. DMZ’s provide
either a transit mechanism from a secure source to an insecure destination or from an insecure
source to a more secure destination. In some cases, a screened subnet which is used for
servers accessible from the outside is referred to as a DMZ.

Denial of Service (DOS)
The prevention of authorized access to a system resource or the delaying of system operations
and functions; usually accomplished by overwhelming the host or server with more requests
than it can handle, disabling the servicing of all of the requests.

Dictionary Attack
An attack that tries all of the phrases or words in a dictionary, trying to crack a password or key.
A dictionary attack uses a predefined list of words compared to a brute force attack that tries all
possible combinations.

Digital Certificate
A digital certificate is an electronic “credit card” that establishes your credentials when doing
business or other transactions on the Web. It is issued by a certification authority. It contains
your name, a serial number, expiration dates, a copy of the certificate holder’s public key (used
for encrypting messages and digital signatures), and the digital signature of the certificateissuing
authority so that a recipient can verify that the certificate is real.

Digital Signature
A digital signature is a hash of a message that uniquely identifies the sender of the message
and proves the message hasn’t changed since transmission.

Digital Signature Algorithm (DSA)
An asymmetric cryptographic algorithm that produces a digital signature in the form of a pair of
large numbers. The signature is computed using rules and parameters such that the identity of
the signer and the integrity of the signed data can be verified.

Digital Signature Standard (DSS)
The US Government standard that specifies the Digital Signature Algorithm (DSA), which
involves asymmetric cryptography.

Disaster Recovery Plan (DRP)
A Disaster Recovery Plan is the process of recovery of IT systems in the event of a disruption or
disaster.

Discretionary Access Control (DAC)
Discretionary Access Control consists of something the user can manage, such as a document
password.

Disruption
A circumstance or event that interrupts or prevents the correct operation of system services and
functions.

Domain Hijacking
Domain hijacking is an attack by which an attacker takes over a domain by first blocking access
to the domain’s DNS server and then putting his own server up in its place

Due Care
Due care ensures that a minimal level of protection is in place in accordance with the best
practice in the industry.

Due Diligence
Due diligence is the requirement that organizations must develop and deploy a protection plan
to prevent fraud, abuse, and additional deploy a means to detect them if they occur.

DumpSec
DumpSec is a security tool that dumps a variety of information about a system’s users, file
system, registry, permissions, password policy, and services.

Dumpster Diving
Dumpster Diving is obtaining passwords and corporate directories by searching through
discarded media.

Eavesdropping
Eavesdropping is simply listening to a private conversation which may reveal information
which can provide access to a facility or network.

Encapsulation
The inclusion of one data structure within another structure so that the first data structure is
hidden for the time being.

Encryption
Cryptographic transformation of data (called “plaintext”) into a form (called “cipher text”)
that conceals the data’s original meaning to prevent it from being known or used.

Escrow Passwords
Escrow Passwords are passwords that are written down and stored in a secure location (like a
safe) that are used by emergency personnel when privileged personnel are unavailable.

Exposure
A threat action whereby sensitive data is directly released to an unauthorized entity.

Extensible Authentication Protocol (EAP)
A framework that supports multiple, optional authentication mechanisms for PPP, including
clear-text passwords, challenge-response, and arbitrary dialog sequences.

False Rejects
False Rejects are when an authentication system fails to recognize a valid user.

Fast Flux
Protection method used by botnets consisting of a continuous and fast change of the DNS
records for a domain name through different IP addresses.

File Transfer Protocol (FTP)
A TCP/IP protocol specifying the transfer of text or binary files across the network.

Filter
A filter is used to specify which packets will or will not be used. It can be used in sniffers to
determine which packets get displayed, or by firewalls to determine which packets get blocked.

Firewall
A logical or physical discontinuity in a network to prevent unauthorized access to data or
resources.

Flooding
An attack that attempts to cause a failure in (especially, in the security of) a computer system or
other data processing entity by providing more input than the entity can process properly.

Form-Based Authentication
Form-Based Authentication uses forms on a webpage to ask a user to input username and
password information.

Forward Lookup
Forward lookup uses an Internet domain name to find an IP address

Fragment Overlap Attack
A TCP/IP Fragmentation Attack that is possible because IP allows packets to be broken down
into fragments for more efficient transport across various media. The TCP packet (and its
header) are carried in the IP packet. In this attack the second fragment contains incorrect offset.
When packet is reconstructed, the port number will be overwritten.

Fragmentation
The process of storing a data file in several “chunks” or fragments rather than in a single
contiguous sequence of bits in one place on the storage medium.

False Rejects
False Rejects are when an authentication system fails to recognize a valid user.

Fast Flux
Protection method used by botnets consisting of a continuous and fast change of the DNS
records for a domain name through different IP addresses.

File Transfer Protocol (FTP)
A TCP/IP protocol specifying the transfer of text or binary files across the network.

Filter
A filter is used to specify which packets will or will not be used. It can be used in sniffers to
determine which packets get displayed, or by firewalls to determine which packets get blocked.

Firewall
A logical or physical discontinuity in a network to prevent unauthorized access to data or
resources.

Flooding
An attack that attempts to cause a failure in (especially, in the security of) a computer system or
other data processing entity by providing more input than the entity can process properly.

Form-Based Authentication
Form-Based Authentication uses forms on a webpage to ask a user to input username and
password information.

Forward Lookup
Forward lookup uses an Internet domain name to find an IP address

Fragment Overlap Attack
A TCP/IP Fragmentation Attack that is possible because IP allows packets to be broken down
into fragments for more efficient transport across various media. The TCP packet (and its
header) are carried in the IP packet. In this attack the second fragment contains incorrect offset.
When packet is reconstructed, the port number will be overwritten.

Fragmentation
The process of storing a data file in several “chunks” or fragments rather than in a single
contiguous sequence of bits in one place on the storage medium.

Frames
Data that is transmitted between network points as a unit complete with addressing and
necessary protocol control information. A frame is usually transmitted serial bit by bit and
contains a header field and a trailer field that “frame” the data. (Some control frames contain no
data.)

Full Duplex
A type of duplex communications channel which carries data in both directions at once. Refers
to the transmission of data in two directions simultaneously. Communications in which both
sender and receiver can send at the same time.

Fully-Qualified Domain Name
A Fully-Qualified Domain Name is a server name with a hostname followed by the full domain
name.

Fuzzing
The use of special regression testing tools to generate out-of-spec input for an application in
order to find security vulnerabilities. Also see “regression testing”.

Gateway
A network point that acts as an entrance to another network.

GNU
GNU is a Unix-like operating system that comes with source code that can be copied, modified,
and redistributed. The GNU project was started in 1983 by Richard Stallman and others, who
formed the Free Software Foundation.

Hardening
Hardening is the process of identifying and fixing vulnerabilities on a system.

Hash Functions
Cryptographic hash functions are used to generate a one way “check sum” for a larger text,
which is not trivially reversed. The result of this hash function can be used to validate if a larger
file has been altered, without having to compare the larger files to each other. Frequently used
hash functions are MD5 and SHA1.

Header
A header is the extra information in a packet that is needed for the protocol stack to process the
packet.

Hijack Attack
A form of active wiretapping in which the attacker seizes control of a previously established
communication association.

Honey Pot
Programs that simulate one or more network services that you designate on your computer’s
ports. An attacker assumes you’re running vulnerable services that can be used to break into
the machine. A honey pot can be used to log access attempts to those ports including the
attacker’s keystrokes. This could give you advanced warning of a more concerted attack.

Host
Any computer that has full two-way access to other computers on the Internet. Or a computer
with a web server that serves the pages for one or more Web sites.

HTTPS
When used in the first part of a URL (the part that precedes the colon and specifies an access
scheme or protocol), this term specifies the use of HTTP enhanced by a security mechanism,
which is usually SSL.

Hub
A hub is a network device that operates by repeating data that it receives on one port to all the
other ports. As a result, data transmitted by one host is retransmitted to all other hosts on the
hub.

Hybrid Attack
A Hybrid Attack builds on the dictionary attack method by adding numerals and symbols to
dictionary words.

Hybrid Encryption
An application of cryptography that combines two or more encryption algorithms, particularly a
combination of symmetric and asymmetric encryption.

Hyperlink
In hypertext or hypermedia, an information object (such as a word, a phrase, or an image;
usually highlighted by color or underscoring) that points (indicates how to connect) to related
information that is located elsewhere and can be retrieved by activating the link.

Hypertext Markup Language (HTML)
The set of markup symbols or codes inserted in a file intended for display on a World Wide Web
browser page.

Hypertext Transfer Protocol HTTP)
The protocol in the Internet Protocol (IP) family used to transport hypertext documents across
an internet.

Identity
Identity is whom someone or what something is, for example, the name by which something is known.

Incident
An incident as an adverse network event in an information system or network or the threat of the occurrence of such an event.

Incident Handling
Incident Handling is an action plan for dealing with intrusions, cyber-theft, denial of service, fire,
floods, and other security-related events. It is comprised of a six step process: Preparation,
Identification, Containment, Eradication, Recovery, and Lessons Learned.

Incremental Backups
Incremental backups only backup the files that have been modified since the last backup. If
dump levels are used, incremental backups only backup files changed since last backup of a
lower dump level.

Ingress Filter
Ingress Filtering is filtering inbound traffic.

Input Validation Attacks
Input Validations Attacks are where an attacker intentionally sends unusual input in the hopes of
confusing an application.

Integrity
Integrity is the need to ensure that information has not been changed accidentally or
deliberately, and that it is accurate and complete.

Integrity Star Property
In Integrity Star Property a user cannot read data of a lower integrity level then their own.

Internet
A term to describe connecting multiple separate networks together.

Internet Control Message Protocol (ICMP)
An Internet Standard protocol that is used to report error conditions during IP datagram
processing and to exchange other information concerning the state of the IP network.

Internet Engineering Task Force (IETF)
The body that defines standard Internet operating protocols such as TCP/IP. The IETF is
supervised by the Internet Society Internet Architecture Board (IAB). IETF members are drawn
from the Internet Society’s individual and organization membership.

Internet Message Access Protocol (IMAP)
A protocol that defines how a client should fetch mail from and return mail to a mail server.
IMAP is intended as a replacement for or extension to the Post Office Protocol (POP). It is
defined in RFC 1203 (v3) and RFC 2060 (v4).

Internet Protocol (IP)
The method or protocol by which data is sent from one computer to another on the Internet.

Intranet
A computer network, especially one based on Internet technology, that an organization uses for
its own internal, and usually private, purposes and that is closed to outsiders.

Intrusion Detection
A security management system for computers and networks. An IDS gathers and analyzes
information from various areas within a computer or a network to identify possible security
breaches, which include both intrusions (attacks from outside the organization) and misuse
(attacks from within the organization).

IP Address
A computer’s inter-network address that is assigned for use by the Internet Protocol and other
protocols. An IP version 4 address is written as a series of four 8-bit numbers separated by
periods.

IP Flood
A denial of service attack that sends a host more echo request (“ping”) packets than the
protocol implementation can handle.

IP Forwarding
IP forwarding is an Operating System option that allows a host to act as a router. A system that
has more than 1 network interface card must have IP forwarding turned on in order for the
system to be able to act as a router.

IP Spoofing
The technique of supplying a false IP address.

ISO
International Organization for Standardization, a voluntary, non-treaty, non-government
organization, established in 1947, with voting members that are designated standards bodies of
participating nations and non-voting observer organizations.

Jitter
Jitter or Noise is the modification of fields in a database while preserving the aggregate
characteristics of that make the database useful in the first place.

Jump Bag
A Jump Bag is a container that has all the items necessary to respond to an incident inside to
help mitigate the effects of delayed reactions.

Kerberos
A system developed at the Massachusetts Institute of Technology that depends on passwords and symmetric cryptography (DES) to implement ticket-based, peer entity authentication service and access control service distributed in a client-server network environment.

Kernal
The essential center of a computer operating system, the core that provides basic services for all other parts of the operating system. A synonym is nucleus. A kernel can be contrasted with a shell, the outermost part of an operating system that interacts with user commands. Kernel and shell are terms used more frequently in Unix and some other operating systems than in IBM mainframe systems.

Lattice Technigues
Lattice Techniques use security designations to determine access to information.

Layer 2 Forwarding Protocol (L2F)
An Internet protocol (originally developed by Cisco Corporation) that uses tunneling of PPP over
IP to create a virtual extension of a dial-up link across a network, initiated by the dial-up server
and transparent to the dial-up user.

Layer 2 Tunneling Protocol (L2TP)
An extension of the Point-to-Point Tunneling Protocol used by an Internet service provider to
enable the operation of a virtual private network over the Internet.

Least Privilege
Least Privilege is the principle of allowing users or applications the least amount of permissions
necessary to perform their intended function.

Lightweight Directory Access Protocol (LDAP)
A software protocol for enabling anyone to locate organizations, individuals, and other
resources such as files and devices in a network, whether on the public Internet or on a
corporate Intranet.

Link State
With link state, routes maintain information about all routers and router-to-router links within a
geographic area, and creates a table of best routes with that information.

List Based Access Control
List Based Access Control associates a list of users and their privileges with each object.

Loadable Kernel Modules (LKM)
Loadable Kernel Modules allow for the adding of additional functionality directly into the kernel
while the system is running.

Log Clipping
Log clipping is the selective removal of log entries from a system log to hide a compromise.

Logic Bombs
Logic bombs are programs or snippets of code that execute when a certain predefined event
occurs. Logic bombs may also be set to go off on a certain date or when a specified set of
circumstances occurs.

Loopback Address
The loopback address (127.0.0.1) is a pseudo IP address that always refer back to the local
host and are never sent out onto a network.

MAC Address
A physical address; a numeric value that uniquely identifies that network device from every
other device on the planet.

Malicious Code
Software (e.g., Trojan horse) that appears to perform a useful or desirable function, but actually
gains unauthorized access to system resources or tricks a user into executing other malicious
logic.

Malware
A generic term for a number of different types of malicious code, including computer viruses.

Mandatory Access Control (MAC)
Mandatory Access Control controls is where the system controls access to resources based on
classification levels assigned to both the objects and the users. These controls cannot be
changed by anyone.

Masquerade Attack
A type of attack in which one system entity illegitimately poses as (assumes the identity of)
another entity.

MD5 Hash
A one way cryptographic hashing function. Also see “hash functions” and “SHA-1”

Measures of Effectiveness (MOE)
Measures of Effectiveness is a probability model based on engineering concepts that allows one
to approximate the impact a give action will have on an environment. In Information warfare it is
the ability to attack or defend within an Internet environment.

Monoculture
Monoculture is the case where a large number of users run the same software, and are
vulnerable to the same attacks.

Morris Worm
A worm program written by Robert T. Morris, Jr. that flooded the ARPANET in November, 1988,
causing problems for thousands of hosts.

Multi-Cast
Broadcasting from one host to a given set of multiple hosts.

Multi-Homed
You are “multi-homed” if your network is directly connected to two or more ISP’s.

Multiplexing
To combine multiple signals from possibly disparate sources, in order to transmit them over a
single path.

NAT
Network Address Translation. It is used to share one or a small number of publicly routable IP addresses among a larger number of hosts. The hosts are assigned private IP addresses, which are then “translated” into one of the publicly routed IP addresses. Typically home or small business networks use NAT to share a single DLS or Cable modem IP address. However, in some cases NAT is used for servers as an additional layer of protection.

National Institute of Standards and Technologies (NIST)
National Institute of Standards and Technology, a unit of the US Commerce Department. Formerly known as the National Bureau of Standards, NIST promotes and maintains measurement standards. It also has active programs for encouraging and assisting industry and science to develop and use these standards.

Natural Disaster
Any “act of God” (e.g., fire, flood, earthquake, lightning, or wind) that disables a system component.

Netmask
32-bit number indicating the range of IP addresses residing on a single IP network/subnet/supernet. This specification displays network masks as hexadecimal numbers. For example, the network mask for a class C IP network is displayed as 0xffffff00. Such a mask is often displayed elsewhere in the literature as 255.255.255.0.

Network Address Translation
The translation of an Internet Protocol address used within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside.

Network Mapping
To compile an electronic inventory of the systems and the services on your network.

Network Taps
Network taps are hardware devices that hook directly onto the network cable and send a copy of the traffic that passes through it to one or more other networked devices.

Network-Based IDS
A network-based IDS system monitors the traffic on its network segment as a data source. This is generally accomplished by placing the network interface card in promiscuous mode to capture all network traffic that crosses its network segment. Network traffic on other segments, and traffic on other means of communication (like phone lines) can’t be monitored. Network-based IDS involves looking at the packets on the network as they pass by some sensor. The sensor can only see the packets that happen to be carried on the network segment it’s attached to. Packets are considered to be of interest if they match a signature. Network-based intrusion detection passively monitors network activity for indications of attacks.Network monitoring offers several advantages over traditional host-based intrusion detection systems. Because many intrusions occur over networks at some point, and because networks are increasingly becoming the targets of attack, these techniques are an excellent method of detecting many attacks which may be missed by host-based intrusion detection mechanisms.

Non-Repudiation
Non-repudiation is the ability for a system to prove that a specific user and only that specific user sent a message and that it hasn’t been modified.

Null Session
Known as Anonymous Logon, it is a way of letting an anonymous user retrieve information such as user names and shares over the network or connect without authentication. It is used by applications such as explorer.exe to enumerate shares on remote servers.

Octet
In digital computer language and Octet is a sequence of eight bits; an eight-bit byte.

One-Way Encryption
Irreversible transformation of plaintext to cipher text, such that the plaintext cannot be recovered from the cipher text by other than exhaustive procedures even if the cryptographic key is known.

One-Way Function
A (mathematical) function, f, which is easy to compute the output based on a given input. However given only the output value it is impossible (except for a brute force attack) to figure out what the input value is.

Open Shortest Path First (OSPF)
Open Shortest Path First is a link state routing algorithm used in interior gateway routing. Routers maintain a database of all routers in the autonomous system with links between the routers, link costs, and link states (up and down).

OSI
OSI (Open Systems Interconnection) is a standard description or “reference model” for how messages should be transmitted between any two points in a telecommunication network. Its purpose is to guide product implementers so that their products will consistently work with other products. The reference model defines seven layers of functions that take place at each end of a communication. Although OSI is not always strictly adhered to in terms of keeping related functions together in a well-defined layer, many if not most products involved in telecommunication make an attempt to describe themselves in relation to the OSI model. It is also valuable as a single reference view of communication that furnishes everyone a common ground for education and discussion.

OSI Layers
The main idea in OSI is that the process of communication between two end points in a telecommunication network can be divided into layers, with each layer adding its own set of special, related functions. Each communicating user or program is at a computer equipped with these seven layers of function. So, in a given message between users, there will be a flow of data through each layer at one end down through the layers in that computer and, at the other end, when the message arrives, another flow of data up through the layers in the receiving computer and ultimately to the end user or program. The actual programming and hardware that furnishes these seven layers of function is usually a combination of the computer operating system, applications (such as your Web browser), TCP/IP or alternative transport and network protocols, and the software and hardware that enable you to put a signal on one of the lines attached to your computer. OSI divides telecommunication into seven layers. The layers are in two groups. The upper four layers are used whenever a message passes from or to a user. The lower three layers (up to the network layer) are used when any message passes through the host computer or router. Messages intended for this computer pass to the upper layers. Messages destined for some other host are not passed up to the upper layers but are forwarded to another host. The seven layers are: Layer 7: The application layer…This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions.) Layer 6: The presentation layer…This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). Sometimes called the syntax layer. Layer 5: The session layer…This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination. Layer 4: The transport layer…This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer. Layer 3: The network layer…This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). The network layer does routing and forwarding. Layer 2: The data-link layer…This layer provides synchronization for the physical level and does bit-stuffing for strings of 1’s in excess of 5. It furnishes transmission protocol knowledge and management. Layer 1: The physical layer…This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.

Overload
Hindrance of system operation by placing excess burden on the performance capabilities of a system component.

Packet
A piece of a message transmitted over a packet-switching network. One of the key features of a packet is that it contains the destination address in addition to the data. In IP networks, packets are often called datagrams.

Packet Switched Network
A packet switched network is where individual packets each follow their own paths through the network from one endpoint to another.

Password Authentication Protocol (PAP)
Password Authentication Protocol is a simple, weak authentication mechanism where a user enters the password and it is then sent across the network, usually in the clear.

Password Cracking
Password cracking is the process of attempting to guess passwords, given the password file information.

Password Sniffing
Passive wiretapping, usually on a local area network, to gain knowledge of passwords.

Patch
A patch is a small update released by a software manufacturer to fix bugs in existing programs.

Patching
Patching is the process of updating software to a different version, usually applying fixes for security vulnerabilities, as well as other fixes for bugs to address performance or user enhancements.

Payload
Payload is the actual application data a packet contains (see Packet).

Penetration
Gaining unauthorized logical access to sensitive data by circumventing a system’s protections.

Penetration Testing
Penetration testing is used to test the external perimeter security of a network or facility.

Permutation
Permutation keeps the same letters but changes the position within a text to scramble the message.

Personal Firewalls
Personal firewalls are those firewalls that are installed and run on individual PCs.

Pharming
This is a more sophisticated form of MITM attack. A user’s session is redirected to a masquerading website. This can be achieved by corrupting a DNS server on the Internet and pointing a URL to the masquerading website’s IP. Almost all users use a URL like  www.worldbank.com instead of the real IP (192.86.99.140) of the website. Changing the pointers on a DNS server, the URL can be redirected to send traffic to the IP of the pseudo website. At the pseudo website, transactions can be mimicked and information like login credentials can be gathered. With this the attacker can access the real www.worldbank.com site and conduct transactions using the credentials of a valid user on that website.

Phishing
The use of e-mails that appear to originate from a trusted source to trick a user into entering valid credentials at a fake website. Typically the e-mail and the web site looks like they are part of a bank the user is doing business with.

Ping of Death
An attack that sends an improperly large ICMP echo request packet (a “ping”) with the intent of overflowing the input buffers of the destination machine and causing it to crash.

Ping Scan
A ping scan scans a network looking for computers that are responding to ICMP Echo Requests.

Ping Sweep
An attack that sends ICMP echo requests (“pings”) to a range of IP addresses, with the goal of finding hosts that can be probed for vulnerabilities.

Plaintext
Ordinary readable text before being encrypted into ciphertext or after being decrypted.

Point-to-Point Protocol (PTP)
A protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. It packages your computer’s TCP/IP packets and forwards them to the server where they can actually be put on the Internet.

Point-to-Point Tunneling Protocol (PPTP)
A protocol (set of communication rules) that allows corporations to extend their own corporate network through private “tunnels” over the public Internet.

Poison Reverse
Split horizon with poisoned reverse (more simply, poison reverse) does include such routes in updates, but sets their metrics to infinity. In effect, advertising the fact that there routes are not reachable.

Polyinstantiation
Polyinstantiation is the ability of a database to maintain multiple records with the same key. It is used to prevent inference attacks.

Polymorphism
Polymorphism is the process by which malicious software changes its underlying code to avoid detection.

Port
A port is nothing more than an integer that uniquely identifies an endpoint of a communication stream. Only one process per machine can listen on the same port number.

Port Scan
A port scan is a series of messages sent by someone attempting to break into a computer to learn which computer network services, each associated with a “well-known” port number, the computer provides. Port scanning, a favorite approach of computer cracker, gives the assailant an idea where to probe for weaknesses. Essentially, a port scan consists of sending a message to each port, one at a time. The kind of response received indicates whether the port is used and can therefore be probed for weakness.

Possession
Possession is the holding, control, and ability to use information.

Post Office Protocol, v3 (POPS)
An Internet Standard protocol by which a client workstation can dynamically access a mailbox on a server host to retrieve mail messages that the server has received and is holding for the client.

Pretty Good Privacy (PG)
Trademark of Network Associates, Inc., referring to a computer program (and related protocols) that uses cryptography to provide data security for electronic mail and other applications on the Internet.

Private Addressing
IANA has set aside three address ranges for use by private or non-Internet connected networks. This is referred to as Private Address Space and is defined in RFC 1918. The reserved address blocks are: 10.0.0.0 to 10.255.255.255 (10/8 prefix) 172.16.0.0 to 172.31.255.255 (172.16/12 prefix) 192.168.0.0 to 192.168.255.255 (192.168/16 prefix)

Program Infector
A program infector is a piece of malware that attaches itself to existing program files.

Program Policy
A program policy is a high-level policy that sets the overall tone of an organization’s security
approach.

Promiscuous Mode
When a machine reads all packets off the network, regardless of who they are addressed to. This is used by network administrators to diagnose network problems, but also by unsavory characters who are trying to eavesdrop on network traffic (which might contain passwords or other information).

Proprietary Information
Proprietary information is that information unique to a company and its ability to compete, such as customer lists, technical data, product costs, and trade secrets.

Protocol
A formal specification for communicating; an IP address the special set of rules that end points in a telecommunication connection use when they communicate. Protocols exist at several levels in a telecommunication connection.

Protocol Stacks (OSI)
A set of network protocol layers that work together.

Proxy Server
A server that acts as an intermediary between a workstation user and the Internet so that the enterprise can ensure security, administrative control, and caching service. A proxy server is associated with or part of a gateway server that separates the enterprise network from the outside network and a firewall server that protects the enterprise network from outside intrusion.

Public Key
The publicly-disclosed component of a pair of cryptographic keys used for asymmetric cryptography.

Public Key Encryption
The popular synonym for “asymmetric cryptography”.

Public Key Infrastructure (PKI)
A PKI (public key infrastructure) enables users of a basically unsecured public network such as the Internet to securely and privately exchange data and money through the use of a public and a private cryptographic key pair that is obtained and shared through a trusted authority. The public key infrastructure provides for a digital certificate that can identify an individual or an organization and directory services that can store and, when necessary, revoke the certificates.

Public-Key Forward Secrecy (PFS)
For a key agreement protocol based on asymmetric cryptography, the property that ensures that a session key derived from a set of long-term public and private keys will not be compromised if one of the private keys is compromised in the future.

QAZ
A network worm.

Race Condition
A race condition exploits the small window of time between a security control being applied and when the service is used.

Reconnaissance
Reconnaissance is the phase of an attack where an attackers finds new systems, maps out networks, and probes for specific, exploitable vulnerabilities.

Registry
The Registry in Windows operating systems in the central set of settings and information required to run the Windows computer.

Regression Testing/Analysis
The use of scripted tests which are used to test software for all possible input is should expect. Typically developers will create a set of regression tests that are executed before a new version of a software is released. Also see “fuzzing”.

Request for Comment (RFC)
A series of notes about the Internet, started in 1969 (when the Internet was the ARPANET). An Internet Document can be submitted to the IETF by anyone, but the IETF decides if the document becomes an RFC. Eventually, if it gains enough interest, it may evolve into an Internet standard.

Resource Exhaustion
Resource exhaustion attacks involve tying up finite resources on a system, making them
unavailable to others.

Reverse Address Resolution Protocol (RARP)
RARP (Reverse Address Resolution Protocol) is a protocol by which a physical machine in a local area network can request to learn its IP address from a gateway server’s Address Resolution Protocol table or cache. A network administrator creates a table in a local area network’s gateway router that maps the physical machine (or Media Access Control – MAC address) addresses to corresponding Internet Protocol addresses. When a new machine is set up, its RARP client program requests from the RARP server on the router to be sent its IP address. Assuming that an entry has been set up in the router table, the RARP server will return the IP address to the machine which can store it for future use.

Reverse Engineering
Acquiring sensitive data by disassembling and analyzing the design of a system component.

Reverse Lookup
Find out the hostname that corresponds to a particular IP address. Reverse lookup uses an IP (Internet Protocol) address to find a domain name.

Reverse Proxy
Reverse proxies take public HTTP requests and pass them to back-end webservers to send the content to it, so the proxy can then send the content to the end-user.

Risk
Risk is the product of the level of threat with the level of vulnerability. It establishes the likelihood of a successful attack.

Risk Assessment
A Risk Assessment is the process by which risks are identified and the impact of those risks determined.

Rivest-Shamir-Adleman (RSA)
An algorithm for asymmetric cryptography, invented in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman.

Role Based Access Control
Role based access control assigns users to roles based on their organizational functions and determines authorization based on those roles.

Root
Root is the name of the administrator account in Unix systems.

Rootkit
A collection of tools (programs) that a hacker uses to mask intrusion and obtain administrator level access to a computer or computer network.

Router
Routers interconnect logical networks by forwarding information to other networks based upon IP addresses.

Routing Information Protocol (RIP)
Routing Information Protocol is a distance vector protocol used for interior gateway routing which uses hop count as the sole metric of a path’s cost.

Routing Loop
A routing loop is where two or more poorly configured routers repeatedly exchange the same
packet over and over.

RPC Scans
RPC scans determine which RPC services are running on a machine.

Rule Set Based Access Control (RSBAC)
Rule Set Based Access Control targets actions based on rules for entities operating on objects.

S/Key
A security mechanism that uses a cryptographic hash function to generate a sequence of 64-bit, one-time passwords for remote user login. The client generates a one-time password by applying the MD4 cryptographic hash function multiple times to the user’s secret key. For each successive authentication of the user, the number of hash applications is reduced by one.

Safety
Safety is the need to ensure that the people involved with the company, including employees, customers, and visitors, are protected from harm.

Scavenging
Searching through data residue in a system to gain unauthorized knowledge of sensitive data.

Secure Electronic Transactions (SET)
Secure Electronic Transactions is a protocol developed for credit card transactions in which all parties (customers, merchant, and bank) are authenticated using digital signatures, encryption protects the message and provides integrity, and provides end-to-end security for credit card transactions online.

Secure Shell (SSH)
A program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another.

Secure Sockets Layer (SSL)
A protocol developed by Netscape for transmitting private documents via the Internet. SSL works by using a public key to encrypt data that’s transferred over the SSL connection.

Security Policy
A set of rules and practices that specify or regulate how a system or organization provides security services to protect sensitive and critical system resources.

Segment
Segment is another name for TCP packets; in computer networking, a segment represents a portion of the network which has been segmented from the rest of the network.

Sensitive Information
Sensitive information, as defined by the federal government, is any unclassified information that, if compromised, could adversely affect the national interest or conduct of federal initiatives.

Separation of Duties
Separation of duties is the principle of splitting privileges among multiple individuals or systems.

Server
A system entity that provides a service in response to requests from other system entities called clients.

Session
A session is a virtual connection between two hosts by which network traffic is passed.

Session Hijacking
Take over a session that someone else has established.

Session Key
In the context of symmetric encryption, a key that is temporary or is used for a relatively short period of time. Usually, a session key is used for a defined period of communication between two computers, such as for the duration of a single connection or transaction set, or the key is used in an application that protects relatively large amounts of data and, therefore, needs to be re-keyed frequently.

SHA1 or SHA-1
A one way cryptographic hash function. Also see “MD5”

Shadow Password File
A system file in which encryption user password are stored so that they aren’t available to
people who try to break into the system.

Share
A share is a resource made public on a machine, such as a directory (file share) or printer
(printer share).

Shell
A Unix term for the interactive user interface with an operating system. The shell is the layer of programming that understands and executes the commands a user enters. In some systems, the shell is called a command interpreter. A shell usually implies an interface with a command syntax (think of the DOS operating system and its “C:>” prompts and user commands such as “dir” and “edit”).

Signal Analysis
Gaining indirect knowledge of communicated data by monitoring and analyzing a signal that is
emitted by a system and that contains the data but is not intended to communicate the data.

Signature
A Signature is a distinct pattern in network traffic that can be identified to a specific tool or exploit.

Single Integrity Property
In Simple Integrity Property a user cannot write data to a higher integrity level than their own.

Simple Network Management Protocol
The protocol governing network management and the monitoring of network devices and their functions. A set of protocols for managing complex networks.

Simple Security Property
In Simple Security Property a user cannot read data of a higher classification than their own.

Smartcard
A smartcard is an electronic badge that includes a magnetic strip or chip that can record and replay a set key.

Smurf
The Smurf attack works by spoofing the target address and sending a ping to the broadcast address for a remote network, which results in a large amount of ping replies being sent to the target.

Sniffer
A sniffer is a tool that monitors network traffic as it received in a network interface.

Sniffing
A synonym for “passive wiretapping.”

Social Engineering
A euphemism for non-technical or low-technology means – such as lies, impersonation, tricks, bribes, blackmail, and threats – used to attack information systems.

Socket
The socket tells a host’s IP stack where to plug in a data stream so that it connects to the right application.

Socket Pair
A way to uniquely specify a connection, i.e., source IP address, source port, destination IP address, destination port.

SOCKS
A protocol that a proxy server can use to accept requests from client users in a company’s network so that it can forward them across the Internet. SOCKS uses sockets to represent and keep track of individual connections. The client side of SOCKS is built into certain Web browsers and the server side can be added to a proxy server.

Software
Computer programs (which are stored in and executed by computer hardware) and associated data (which also is stored in the hardware) that may be dynamically written or modified during execution.

Source Port
The port that a host uses to connect to a server. It is usually a number greater than or equal to 1024. It is randomly generated and is different each time a connection is made.

Spam
Electronic junk mail or junk newsgroup postings.

Spanning Port
Configures the switch to behave like a hub for a specific port.

Split Horizon
Split horizon is a algorithm for avoiding problems caused by including routes in updates sent to the gateway from which they were learned.

Split Key
A cryptographic key that is divided into two or more separate data items that individually convey
no knowledge of the whole key that results from combining the items.

Spoof
Attempt by an unauthorized entity to gain access to a system by posing as an authorized user.

SQL Injection
SQL injection is a type of input validation attack specific to database-driven applications where SQL code is inserted into application queries to manipulate the database.

Stack Mashing
Stack mashing is the technique of using a buffer overflow to trick a computer into executing arbitrary code.

Star Property
In Star Property, a user cannot write data to a lower classification level without logging in at that lower classification level.

State Machine
A system that moves through a series of progressive conditions.

Stateful Inpsection
Also referred to as dynamic packet filtering. Stateful inspection is a firewall architecture that works at the network layer. Unlike static packet filtering, which examines a packet based on the information in its header, stateful inspection examines not just the header information but also the contents of the packet up through the application layer in order to determine more about the packet than just information about its source and destination.

Static Host Tables
Static host tables are text files that contain hostname and address mapping.

Static Routing
Static routing means that routing table entries contain information that does not change.

Stealthing
Stealthing is a term that refers to approaches used by malicious code to conceal its presence on the infected system.

Steganalysis
Steganalysis is the process of detecting and defeating the use of steganography.

Steganography
Methods of hiding the existence of a message or other data. This is different than cryptography, which hides the meaning of a message but does not hide the message itself. An example of a steganographic method is “invisible” ink.

Store-and-Forward
Store-and-Forward is a method of switching where the entire packet is read by a switch to
determine if it is intact before forwarding it.

Stream Cipher
A stream cipher works by encryption a message a single bit, byte, or computer word at a time.

Strong Star Property
In Strong Star Property, a user cannot write data to higher or lower classifications levels than their own.

Sub Network
A separately identifiable part of a larger network that typically represents a certain limited number of host computers, the hosts in a building or geographic area, or the hosts on an individual local area network.

Subnet Mask
A subnet mask (or number) is used to determine the number of bits used for the subnet and host portions of the address. The mask is a 32-bit value that uses one-bits for the network and subnet portions and zero-bits for the host portion.

Switch
A switch is a networking device that keeps track of MAC addresses attached to each of its ports so that data is only transmitted on the ports that are the intended recipient of the data.

Switched Network
A communications network, such as the public switched telephone network, in which any user may be connected to any other user through the use of message, circuit, or packet switching and control devices. Any network providing switched communications service.

Symbolic Links
Special files which point at another file.

Symmetric Cryptography
A branch of cryptography involving algorithms that use the same key for two different steps of the algorithm (such as encryption and decryption, or signature creation and signature verification). Symmetric cryptography is sometimes called “secret-key cryptography” (versus public-key cryptography) because the entities that share the key.

Symmetric Key
A cryptographic key that is used in a symmetric cryptographic algorithm.

SYN Flood
A denial of service attack that sends a host more TCP SYN packets (request to synchronize sequence numbers, used when opening a connection) than the protocol implementation can handle.

Synchronization
Synchronization is the signal made up of a distinctive pattern of bits that network hardware looks for to signal that start of a frame.

Syslog
Syslog is the system logging facility for Unix systems.

System Security Officer (SSO)
A person responsible for enforcement or administration of the security policy that applies to the system.

System-Specific Policy
A System-specific policy is a policy written for a specific system or device.

T1, T3
A digital circuit using TDM (Time-Division Multiplexing).

Tamper
To deliberately alter a system’s logic, data, or control information to cause the system to perform unauthorized functions or services.

TCP Fingerprinting
TCP fingerprinting is the user of odd packet header combinations to determine a remote operating system.

TCP Full Open Scan
TCP Full Open scans check each port by performing a full three-way handshake on each port to determine if it was open.

TCP Half Open Scan
TCP Half Open scans work by performing the first half of a three-way handshake to determine if a port is open.

TCP Wrapper
A software package which can be used to restrict access to certain network services based on the source of the connection; a simple tool to monitor and control incoming network traffic.

TCP/IP
A synonym for “Internet Protocol Suite;” in which the Transmission Control Protocol and the Internet Protocol are important parts. TCP/IP is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an Intranet or an Extranet).

TCPDump
TCPDump is a freeware protocol analyzer for Unix that can monitor network traffic on a wire.

TELNET
A TCP-based, application-layer, Internet Standard protocol for remote login from one host to another.

Threat
A potential for violation of security, which exists when there is a circumstance, capability, action, or event that could breach security and cause harm.

Threat Assessment
A threat assessment is the identification of types of threats that an organization might be exposed to.

Threat Model
A threat model is used to describe a given threat and the harm it could to do a system if it has  vulnerability.

Threat Vector
The method a threat uses to get to the target.

Time-to-Live
A value in an Internet Protocol packet that tells a network router whether or not the packet has been in the network too long and should be discarded.

Tiny Fragment Attack
With many IP implementations it is possible to impose an unusually small fragment size on outgoing packets. If the fragment size is made small enough to force some of a TCP packet’s TCP header fields into the second fragment, filter rules that specify patterns for those fields will not match. If the filtering implementation does not enforce a minimum fragment size, a disallowed packet might be passed because it didn’t hit a match in the filter. STD 5, RFC 791 states: Every Internet module must be able to forward a datagram of 68 octets without further fragmentation. This is because an Internet header may be up to 60 octets, and the minimum fragment is 8 octets.

Token Ring
A token ring network is a local area network in which all computers are connected in a ring or star topology and a binary digit or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time.

Token-Based Access Control
Token based access control associates a list of objects and their privileges with each user. (The opposite of list based.)

Token-Based Devices
A token-based device is triggered by the time of day, so every minute the password changes, requiring the user to have the token with them when they log in.

Topology
The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a network. Note 1: Two networks have the same topology if the connection configuration is the same, although the networks may differ in physical interconnections, distances between nodes, transmission rates, and/or signal types. Note 2: The common types of network topology are illustrated.

Traceroute (tracert.exe)
Traceroute is a tool the maps the route a packet takes from the local machine to a remote destination.

Transmission Control Protocol (TCP)
A set of rules (protocol) used along with the Internet Protocol to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet. Whereas the IP rotocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.

Transport Layer Security (TLS)
A protocol that ensures privacy between communicating applications and their users on the Internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message. TLS is the successor to the Secure Sockets Layer.

Triple DES
A block cipher, based on DES, that transforms each 64-bit plaintext block by applying the Data Encryption Algorithm three successive times, using either two or three different keys, for an effective key length of 112 or 168 bits.

Triple-Wrapped
S/MIME usage: data that has been signed with a digital signature, and then encrypted, and then signed again.

Trojan Horse
A computer program that appears to have a useful function, but also has a hidden and potentially malicious function that evades security mechanisms, sometimes by exploiting legitimate authorizations of a system entity that invokes the program.

Trunking
Trunking is connecting switched together so that they can share VLAN information between them.

Trust
Trust determine which permissions and what actions other systems or users can perform on remote machines.

Trusted Ports
Trusted ports are ports below number 1024 usually allowed to be opened by the root user.

Tunnel
A communication channel created in a computer network by encapsulating a communication protocol’s data packets in (on top of) a second protocol that normally would be carried above, or at the same layer as, the first one. Most often, a tunnel is a logical point-to-point link – i.e., an OSI layer 2 connection – created by encapsulating the layer 2 protocol in a transport protocol (such as TCP), in a network or inter-network layer protocol (such as IP), or in another link layer protocol. Tunneling can move data between computers that use a protocol not supported by the network connecting them.

UDP Scan
UDP scans perform scans to determine which UDP ports are open.

Unicast
Broadcasting from host to host.

Uniform Resource Identifier (URI)
The generic term for all types of names and addresses that refer to objects on the World Wide Web.

Uniform Resource Locator (URL)
The global address of documents and other resources on the World Wide Web. The first part of the address indicates what protocol to use, and the second part specifies the IP address or the domain name where the resource is located. For example, http://www.pcwebopedia.com/index.html .

Unix
A popular multi-user, multitasking operating system developed at Bell Labs in the early 1970s. Created by just a handful of programmers, Unix was designed to be a small, flexible system used exclusively by programmers.

Unprotected Share
In Windows terminology, a “share” is a mechanism that allows a user to connect to file systems and printers on other systems. An “unprotected share” is one that allows anyone to connect to it.

User
A person, organization entity, or automated process that accesses a system, whether authorized to do so or not.

User Contingency Plan
User contingency plan is the alternative methods of continuing business operations if IT systems are unavailable.

User Datagram Protocol (UDP)
A communications protocol that, like TCP, runs on top of IP networks. Unlike TCP/IP, UDP/IP provides very few error recovery services, offering instead a direct way to send and receive datagrams over an IP network. It’s used primarily for broadcasting messages over a network. UDP uses the Internet Protocol to get a datagram from one computer to another but does not divide a message into packets (datagrams) and reassemble it at the other end. Specifically, UDP doesn’t provide sequencing of the packets that the data arrives in.

Virtual Private Network (VPN)
A restricted-use, logical (i.e., artificial or simulated) computer network that is constructed from the system resources of a relatively public, physical (i.e., real) network (such as the Internet), often by using encryption (located at hosts or gateways), and often by tunneling links of the virtual network across the real network. For example, if a corporation has LANs at several different sites, each connected to the Internet by a firewall, the corporation could create a VPN by (a) using encrypted tunnels to connect from firewall to firewall across the Internet and (b) not allowing any other traffic through the firewalls. A VPN is generally less expensive to build and operate than a dedicated real network, because the virtual network shares the cost of system resources with other users of the real network.

Virus
A hidden, self-replicating section of computer software, usually malicious logic, that propagates by infecting – i.e., inserting a copy of itself into and becoming part of – another program. A virus cannot run by itself; it requires that its host program be run to make the virus active.

Voice Firewall
A physical discontinuity in a voice network that monitors, alerts and controls inbound and outbound voice network activity based on user-defined call admission control (CAC) policies, voice application layer security threats or unauthorized service use violations.

Voice Intrusion Prevention System (VIPS)
Voice IPS is a security management system for voice networks which monitors voice traffic for multiple calling patterns or attack/abuse signatures to proactively detect and prevent toll fraud, Denial of Service, telecom attacks, service abuse, and other anomalous activity.

War Chalking
War chalking is marking areas, usually on sidewalks with chalk, that receive wireless signals that can be accessed.

War Dialer
A computer program that automatically dials a series of telephone numbers to find lines connected to computer systems, and catalogs those numbers so that a cracker can try to break into the systems.

War Dialing
War dialing is a simple means of trying to identify modems in a telephone exchange that may be susceptible to compromise in an attempt to circumvent perimeter security.

War Driving
War driving is the process of traveling around looking for wireless access point signals that can be used to get network access.

Web of Trust
A web of trust is the trust that naturally evolves as a user starts to trust other’s signatures, and the signatures that they trust.

Web Server
A software process that runs on a host computer connected to the Internet to respond to HTTP requests for documents from client web browsers.

WHOIS
An IP for finding information about resources on networks.

Windump
Windump is a freeware tool for Windows that is a protocol analyzer that can monitor network traffic on a wire.

Wired Equivalent Privacy (WEP)
A security protocol for wireless local area networks defined in the standard IEEE 802.11b.

Wireless Application Protocol
The global, hypermedia-based collection of information and services that is available on Internet servers and is accessed by browsers using Hypertext Transfer Protocol and other information retrieval mechanisms.

Wiretapping
Monitoring and recording data that is flowing between two points in a communication system.

World Wide Web (“the Web”, WWW, W3)
The global, hypermedia-based collection of information and services that is available on Internet servers and is accessed by browsers using Hypertext Transfer Protocol and other information retrieval mechanisms.

Worm
A computer program that can run independently, can propagate a complete working version of itself onto other hosts on a network, and may consume computer resources destructively.

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No terms are available for this section.

Zero Day
The “Day Zero” or “Zero Day” is the day a new vulnerability is made known. In some cases, a “zero day” exploit is referred to an exploit for which no patch is available yet. (“day one” – day at which the patch is made available).

Zero-day Attack
A zero-day (or zero-hour or day zero) attack or threat is a computer threat that tries to exploit computer application vulnerabilities that are unknown to others or undisclosed to the software developer. Zero-day exploits (actual code that can use a security hole to carry out an attack) are used or shared by attackers before the software developer knows about the vulnerability.

Zombies
A zombie computer (often shortened as zombie) is a computer connected to the Internet that has been compromised by a hacker, a computer virus, or a trojan horse. Generally, a compromised machine is only one of many in a botnet, and will be used to perform malicious tasks of one sort or another under remote direction. Most owners of zombie computers are unaware that their system is being used in this way. Because the owner tends to be unaware, these computers are metaphorically compared to zombies.