Worm

(1) A program or algorithm that replicates itself over a computer network and usually performs malicious actions, such as using up the computer's resources and possibly shutting the system down. Also see virus.

(2) When used in all capital letters, WORM is an acronym for for write once, read many, an optical disk technology that allows you to write data onto a disk just once. After that, the data is permanent and can be read any number of times.