Creeper and Reaper

Creeper was an experimental computer program written by Bob Thomas at BBN in 1971.

[2] Its original iteration was designed to move between DEC PDP-10 mainframe computers running the TENEX operating system using the ARPANET, with a later version by Ray Tomlinson designed to copy itself between computers rather than simply move.

[6] Reaper was the first anti-virus software, designed to delete Creeper by moving across the ARPANET.

[3] The conflict between Creeper and Reaper served as inspiration for the programming game Core War,[3] while fictionalized versions of Reaper have been used as antagonists in the anime Digimon Tamers[7] and the visual novel Digital: A Love Story.

[8] A humanized Creeper has also appeared in the webcomic Internet Explorer, alongside the likewise personified Morris Worm.