PhysOrg has a sweet little story about the jokey birth of what could be the earliest computer virus:
He developed what is now known as a “boot sector” virus. When it boots, or starts up, an infected disk places a copy of the virus in the computer’s memory. Whenever someone inserts a clean disk into the machine and types the command “catalog” for a list of files, a copy gets written onto that disk as well. The newly infected disk is passed on to other people, other machines and other locations.
The prank, though annoying to victims, is relatively harmless compared with the viruses of today. Every 50th time someone booted an infected disk, a poem he wrote would appear, saying in part, “It will get on all your disks; it will infiltrate your chips.”
Skrenta started circulating the virus in early 1982 among friends at his school and at a local computer club. Years later, he would continue to hear stories of other victims, including a sailor during the first Gulf War nearly a decade later (Why that sailor was still using an Apple II, Skrenta does not know).