Reaper (program)
Reaper was the first anti-virus software. It was created by Ray Tomlinson to move across the ARPANET and delete the transmitting Creeper program. Creeper had been an experimental computer program originally written by Bob Thomas at BBN in 1971. Its original iteration was designed to move between DEC PDP-10 mainframe computers running the TENEX operating system using the ARPANET. A later version by Ray Tomlinson designed to copy itself between computers rather than simply move, thus making Ray Tomlinson the father of the computer worm. Creeper was not malicious but was the first example of a computer  worm. The only effect being a message it output to the teletype reading "I'm the creeper: catch me if you can". Strictly speaking, the second worm introduced on ARPANET was Reaper as it was a worm, meant to delete any instances of Creeper that it could find.