Daemon - A program which is often started at the time the system boots and runs continuously without intervention from any of the users on the system. The daemon program forwards the requests to other programs (or processes) as appropriate. The term daemon is a Unix term, though many other operating systems provide support for daemons, though they're sometimes called other names. Windows, for example, refers to daemons and System Agents and services.
Data Aggregation - Data Aggregation is the ability to get a more complete picture of the information by analyzing several different types of records at once
Data Encryption Standard (DES) - 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 Mining - Data Mining is a technique used to analyze existing information, usually with the intention of pursuing new avenues to pursue business.
Database - A large, regularly updated collection of data that allows access and manipulation by one or multiple users.
DDoS attack - An external assault in which multiple sources attack a system, with the goal of denying service to its users.
Decapsulation - Decapsulation is the process of stripping off one layer's headers and passing the rest of the packet up to the next higher layer on the protocol stack.
Denial of Service - 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.
Dictionary attack - An attack that uses a brute-force technique of trying all of the phrases or words in a dictionary.
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 certificate-issuing authority so that a recipient can verify that the certificate is real.
Digital Envelope - A digital envelope is an encrypted message with the encrypted session key.
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 Standard (DSS) - The US Government standard that specifies the Digital Signature Algorithm (DSA), which involves asymmetric cryptography.
Discretionary Access Control (DAC) - Discretionary Access Control consists of something the user can manage, such as a document password.
Distance Vector - Distance vectors measure the cost of routes to determine the best route to all known networks.
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.
Domain name - A string of letters and numbers used to name organizations, computers and addresses on the Internet.
DoS attack - A malicious attempt to render computer resource unavailable to its users.
Dynamic Link Library - A collection of small programs, any of which can be called when needed by a larger program that is running in the computer. The small program that lets the larger program communicate with a specific device such as a printer or scanner is often packaged as a