Skip to main content
Select Source:



Worms are destructive, self-replicating computer viruses that spread via e-mail. Once a user activates a wormusually by opening an infected file attachmentthe virus makes copies of itself and sends them to some or all of the e-mail addresses in the user's address book. The ability to spread rapidly makes worms especially dangerous, since much damage can be done before infected users know what is happening. By overloading them with messages and eating up system resources like memory, worms cause e-mail servers, computer networks, and stand-alone personal computers to crash. Some worms also erase or alter files. Among the most well-known worms were Worm.ExploreZip, LoveLetter, NewLove, Prilissa, Melissa, Killer Resume, Bubble-boy, Morris, Code Red, and, perhaps most potentially destructive of all, Nimda, which hit in September 2001.

In the early 2000s, the increasing appearance of polymorphic and metamorphic worms, such as Love-Letter, caused concern among both users and those responsible for administering large computer systems. Polymorphic worms have the ability to change their form through the use of encryption. They are programmed to periodically decrypt themselves, change slightly, and then encrypt again to avoid detection by anti-virus software. Metamorphic worms use special tools called mutation engines to periodically create new, slightly different versions of themselves that avoid detection.

In addition to being a nuisance, the damage caused by worms and other viruses results in real costs for companies doing business on the Web, some of which are passed on to consumers in the form of higher costs for products and services. According to InfoWorld, Carlsbad, California-based Computer Economics estimated that companies devoted $7.6 billion to virus attacks in the first half of 1999 alone. Additionally, according to a Network World, article by Ellen Messmer, 41 percent of companies surveyed by the International Computer Security Association (ICSA) said the LoveLetter worm "inflicted a 'disaster' in their networks, shutting down servers and costing companies an average of $120,000 based on productivity and other measures."

Companies devote an increasing amount of resources to the prevention of worms and other viruses. In the early 2000s, along with using anti-virus software, some organizations formed 24-hour virus response teams, wrote emergency response policies, and used virus scanning servers to check the integrity of incoming e-mail messages before they entered computer networks. According to Fontana's article, Portland, Maine-based Fairchild Semiconductor even dropped the use of file attachments and forbids the distribution of executable files via e-mail within the company. While Fairchild's actions may appear to be extreme, such measures may be necessary in an age when, according to the ICSA, virus infections are increasing rapidly.


Fontana, John. "Defending Against Outlook Viruses." Network World, July 3, 2000.

McClure, Stuart, and Joel Scambray. "Virus Threats of Past and Present Reveal Current State of the Digital Immune System." InfoWorld, July 12, 1999.

McNamara, Paul. "Worm Outbreak has Managers Fishing for Answers." Network World, June 21, 1999.

Messmer, Ellen. "Experts Predict More Mutating Viruses." Network World, October 30, 2000.

Riggs, Brian. "New Worm Viruses Threaten Windows PCs." InformationWeek, November 29, 1999.

Schar, Steve. "The Last Laugh." Credit Union Management, September, 1999.

"Worm." Techencyclopedia, February 12, 2001. Available from

SEE ALSO: Computer Crime; Computer Security; Denial of Service Attack; National Information Infrastructure Protection Act of 1996; National Infrastructure Protection Center; Viruses

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Worms." Gale Encyclopedia of E-Commerce. . 19 Jan. 2018 <>.

"Worms." Gale Encyclopedia of E-Commerce. . (January 19, 2018).

"Worms." Gale Encyclopedia of E-Commerce. . Retrieved January 19, 2018 from


worm (or WORM) Acronym for write once, read many (times).
1. A class of storage device in which information, once written, cannot be erased or overwritten. The write-once CD-ROM is an example. See optical storage.

2. A virus-like program that seeks out other connected hosts in a computer network and, by exploiting a vulnerability, transfers itself to them.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"worm." A Dictionary of Computing. . 19 Jan. 2018 <>.

"worm." A Dictionary of Computing. . (January 19, 2018).

"worm." A Dictionary of Computing. . Retrieved January 19, 2018 from