Answer: Creeper

A computer worm is a form of stand alone computer malware that replicates itself, typically across a network, in order to spread itself to other computers. The very first computer worm was an experimental computer program written by Bob Thomas in 1971.

Thomas was working at BBN, a major contractor involved in the early development of ARPANET (the precursor of the modern Internet). Thomas’s version was designed to move itself from DEC PDP-10 mainframe terminal to mainframe terminal, outputting the text “I’m the creeper: catch me if you can”. Ray Tomlinson, another early ARPANET engineer, modified the code so that Creeper didn’t just move itself, but left behind a copy giving it, in the process, the signature behavior of a modern computer worm.

After having their fun with the harmless worm (it didn’t manipulate system files, cause damage, or do anything malicious like modern worms do), Ray Tomlinson wrote a companion worm called “Reaper” that followed behind Creeper and deleted all instances of it.

In addition to being the first computer worm, Creeper (and its nemesis Reaper) served as the inspiration for the 1984 programming game Core War, which pitted battle programs against each other.