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worm: n.

[from tapeworm in John Brunner's novel The Shockwave Rider, via XEROX PARC] A program that propagates itself over a network, reproducing itself as it goes. Compare virus. Nowadays the term has negative connotations, as it is assumed that only crackers write worms. Perhaps the best-known example was Robert T. Morris's Great Worm of 1988, a ‘benign’ one that got out of control and hogged hundreds of Suns and VAXen across the U.S. See also cracker, RTM, Trojan horse, ice.