What was the First Computer Virus?

The first computer virus is widely accepted to be the "Creeper Virus" and occurred in 1971 on ARPANET, the scientific/military network that came before the modern internet. Creeper was an experimental self-replicating program that infected DEC computers across the network — this would be considered a computer worm today.

Written by Bob Thomas at the BBN Technologies lab, Creeper propagated itself throughout ARPANET by exploiting a vulnerability in DEC PDP-10 computers running the TENEX operating system. The worm wasn’t malicious and, upon gaining access to a machine and replicating itself, broadcast “I’m the creeper, catch me if you can!” on the terminal screen. The first virus removal program, dubbed The Reaper, soon followed, designed to ferret out Creeper infections.