The first virus detected was written by Bob Thomas. Called the Creeper it is the oldest known purpose-built virus. The ARPANET was an early version of the internet on the TENEX operating system and it was here where, during the early 1970s, the Creeper sprouted through the system.
It created a message, 'I'm the Creeper, catch me if you can' - no fun to the poor operater. A means of dealing with it was vital. The Reaper program was designed to deal with the wretched Creeper virus.