Creeper (program)

           Creeper was an experimental self-replicating program written by Bob Thomas at BBN in 1971. It was designed not to damage but to demonstrate a mobile application. It is generally accepted to be the first computer worm, although the notion of a "computer virus" did not exist in the 1970s. Creeper infected DEC PDP-10 computers running the TENEX operating system.

Virus:

        Creeper gained access via the ARPANET and copied itself to the remote system where the message, "I'm the creeper, catch me if you can!" was displayed. The Creeper would start to print a file, but then stop, find another Tenex system, open a connection, pick itself up and transfer to the other machine (along with its external state, files, etc.), and then start running on the new machine, displaying the message. The program rarely if ever actually replicated itself; rather, it jumped from one system to another, attempting to remove itself from previous systems as it propagated forward. Thus, Creeper didn't install multiple instances of itself on several targets, it just moseyed around a network.

Reaper:
       The Reaper program was created to delete Creeper.