In 1971, Bob Thomas at BBN Technologies created a self-replicating program, designed to infect servers on ARPANET, the precursor to the internet.
Allegedly named after the Scooby Doo villain, the Creeper Virus infected the remote systems and displayed the message “I’m the creeper, catch me if you can!”.
Ray Tomlinson, who also implemented the first email program and invented the use of the “@” symbol as a means of addressing, wrote a similar self-replicating program called Reaper which deleted Creeper. This could be considered as the first anti-virus software.
Image: ARPANET 1974 By Yngvar [Public domain], via Wikimedia Commons