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Denial of Service (DoS) Attacks
Denial of service attacks are intended to paralyze networks or web sites by overloading them with useless traffic. A denial of service attack is a form of gridlock on the network. The goal of a Denial of Service (DoS) Attack is not to steal information, but to disable a device or network so users no longer have access to network resources.

Dial-up connection
An Internet connection that is established on a regular phone line through a modem.

Digital Certificate
An attachment to an electronic message that verifies that a user sending a message is who he or she claims to be, and to provide the receiver with the means to encode a reply. A digital certificate contains the sender's public key and a variety of other identification information. Digital certificates are issued by a Certificate Authority.

Digital fingerprint
Digital fingerprints use mathematical algorithms to generate a string of digits and numbers that represents the contents of an electronically-transmitted message. If the message is tampered with, the digital fingerprint will change to reflect changes in the content. The fingerprint of the received message can then be compared with the digital fingerprint of the original message to ensure that the contents have not been altered.

Digital Signature
A digital code encrypted with the sender's private key that can be attached to an electronically transmitted message that guarantees the authentic identity of the sender and is unforgeable by other parties. On October 1, 2000 a law passed by the U.S. Congress went into effect giving digital signatures the same legal status as traditional ink signatures.

Distributed Denial of Service (DDoS) Attacks
A Denial of Service attack that the perpetrator launches remotely from numerous machines that have been infiltrated. At a designated command or time, infected host computers send messages to a target computer without the knowledge of the owners of the host computers, which are known as zombies. The volume of messages arriving over the Internet effectively knocks out the target server, making the Web site inaccessible to other Net surfers.

DNS or Domain Name System
An Internet service that translates a domain name into its corresponding IP address so that the desired computer system can be found and communicated with.

Domain Name
The linguistic code that represents an IP address. Domain names are used instead of IP addresses for the simple reason that for humans names are easier to remember than numbers. Domain names are used in URLs to identify particular Web pages, such as Network applications receive a domain name from user input and then request the appropriate IP address from a Domain Name Server. Domain names are then translated to the appropriate IP address. At the broadest level, the Internet consists of several 'top-level' domains, each of which can be identified by the final two or three letters in the domain name. Examples of top-level domains are .com (used by businesses), .edu (used by schools) and .org (used by non-profit organizations).

"Downloading" a file is the process of accessing a file over the Internet and saving it on your computer. Your browser also downloads Web pages into its cache (temporary memory) to display them.

DSL or Digital Subscriber Line
One of a class of Internet connections known as always-on connections. DSL offers high-speed data transmission over ordinary telephone lines using special modems connected to normal phone lines. One of the advantages of DSL connections over Dial-up connections is that Internet connectivity does not interfere with the use of phone lines.


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