<networking, security> (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 the Great Worm.
Compare Trojan horse.