Monday, November 21, 2005

Worms

A worm is a self-contained program that replicates itself over a computer network, such as the Internet. Worms can conduct this activity without the use of a host file, unlike viruses, which need a host file to spread from computer to computer. Email is a common target for the propagation of worms, but they also spread over network connections and IRC (Internet Relay Chat).
Worms can be relentless in their pursuit to achieve a goal (if there is a finite goal). For example, many worms continue to execute until a computer reboots or shuts down, and even then, they usually start again when a computer restarts.
One of the most damaging worms is Code Red, which exploited vulnerability in servers running Microsoft’s IIS (Internet Information Server). A variant of this crafty worm attacked more than 350,000 servers over several days in July 2001, flooding the Internet with scans for vulnerable computers. When clocks struck midnight (GMT [Greenwich Mean Time]) on July 19, the worm instructed the infected servers to begin a massive DoS (denial of service) attack on a White House Internet hub, creating the potential for blackouts across the Internet. Fortunately, a design flaw left the worm open to counterattack, which successfully shut down Code Red.

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