Worm Definition

A worm is a computer program that replicates itself and is self-propagating.

It is similar to a computer virus in that it makes copies of itself without human intervention. The difference is that a virus attaches itself to, and becomes part of, another executable (i.e., runnable) program, whereas a worm is self-contained and does not need to be part of another program to propagate itself. Also, while viruses are designed to cause problems on a local system and are passed through boot sectors of disks and through e-mail attachments and other files, worms are designed to thrive in a network environment. Once a worm is executed, it seeks other systems, rather than just parts of systems, to infect, and it then copies its code to them.

Worms are almost always designed to do something malicious, such as consuming computer resources, freezing up processes and possibly shutting the system down. A common function of worms is to install back doors in computer, some of which are subsequently used by other worms to gain entry. A back door is any hidden method for bypassing normal authentication or obtaining remote access to a computer or other system. Other functions include relaying spam and slowing down networks.

There has been some discussion about whether worms can also be used for good purposes. For example, a worm was developed to download and install patches from Microsoft's website to repair vulnerabilities in users' systems. Although this such repair was apparently successful, it generated a large amount of network traffic and took place without users' explicit permission. Thus, most computer security experts are apposed to any use of worms regardless of the purpose.

Worms typically infect a system without the user's knowledge, and the first indication that they exist is often a substantial slowdown in performance. The various Microsoft Windows systems are particularly vulnerable to worms, as they are to all malware (i.e., malicious software), but the worms can usually be removed through the use of specialized programs. In contrast, Linux and other Unix-like operating systems, if correctly used, are highly resistant to worms and other malware because they have been designed from the ground up with security as a high priority.

The term worm was taken from John Brunner's 1970s science fiction novel The Shockwave Rider by writers of a paper on experiments in distributed computing because of similarities they observed with their software. The first functioning worm was created in 1978 by two researchers at Xerox PARC.

The first worm to attract widespread attention, and possibly the most famous, was the Morris worm, which was written by Robert Tappan Morris, Jr. at the MIT Artificial intelligence Laboratory. Designed to exploit bugs in BSD UNIX and related systems, it was accidentally released in November 1988, and it quickly infected much of the Internet.