Answer: Creeper

While the technical definitions for computer virus, worm, and malware might have a little overlap, it’s generally accepted that the first type of computer “virus” occurred in 1971 on ARPANET, the scientific/military network that preceded the modern internet. Creeper was an experimental self-replicating program that infected DEC computers across the network.

Written by Bob Thomas at BBN Technologies, Creeper propagated itself throughout ARPANET by exploiting a vulnerability in DEC PDP-10 computers running the TENEX operating system. The worm wasn’t malicious and, upon gaining access to a machine and replicating itself, broadcast “I’m the creeper, catch me if you can!” on the terminal screen. The first virus removal program, dubbed The Reaper, soon followed, designed to ferret out Creeper infections and tidy up.

For years afterwards, Thomas’ handiwork stood out as one of the only examples of a computer virus or anything even remotely similar. Although by modern standards Creeper was a non-malicious worm, at the time, it was the first example of a piece of software propagating itself, acting, in however simplistic a fashion, independently. Once Thomas let it loose, it was off and running.

Today, if a piece of software like Creeper were to appear, our significantly more sophisticated understanding of what constitutes a worm, a virus, a piece of malware, and all their potentially overlapping components, would lead to Creeper being classified differently. None the less, it preceded anything remotely like it by ten years when the next-best competition for the title appeared in the wild in the form of “Elk Cloner”—an Apple II virus that spread by copying itself to floppy disks inserted in infected machines instead of, like Creeper, propagating over a network.