Reaper was the first widely recognized computer antivirus program, created in 1971.
Reaper was designed to find and delete Creeper, an experimental self-replicating program that moved across ARPANET-connected systems. Creeper displayed a message and copied itself between compatible computers, making it an early example of a computer worm rather than a conventional destructive virus.
Unlike modern antivirus software, Reaper was not a commercial security suite with a database of signatures. It was a specialized cleanup program created for the particular threat posed by Creeper. The two programs are therefore often discussed together in histories of malware and cybersecurity.
The story is sometimes simplified by calling Creeper the first computer virus. More precisely, Creeper is generally described as an early worm, while Reaper is remembered as its countermeasure. This distinction matters because worms spread through networks without needing to attach themselves to another executable file.