The Creeper and the first antivirus program
It is generally believed that the first computer virus to be unleashed on vulnerable computers was the Creeper virus. The Creeper virus infected the forerunner of the Internet, a computer network called the ARPANET. This was in the early 1970s. The virus was not malicious in the sense that it did not harm the computers it affected, however on infected machines it displayed the message “I AM THE CREEPER: CATCH ME IF YOU CAN.”
The Creeper was duly captured for what is arguably the first piece of antivirus software ever created. This program was called Reaper (as in Grim Reaper) and it would search for Creeper-infected computers and destroy them properly. The Reaper program was not like the antivirus programs we know today, but it was in fact a virus in its own right, as it automatically replicated and spread across a network. (About a year ago we discovered biological viruses that can infect other biological viruses.)
There are many rumors about the authors of The Creeper and The Reaper, and many suspect that it was the same person. His motivations have been analyzed as possibly a hoax, a scientific experiment that got out of control, and even blackmail. Whoever has managed to keep it away from the general public, which is remarkable in itself.
An alternative possibility is that not one person did it. There was considerable military involvement in the ARPANET network and one aspect of the ARPANET research was to examine whether the system was robust enough to withstand a nuclear war and still provide a communications network. Both The Creeper and The Reaper could have been military experiments to test the vulnerability and protection of the network. This would certainly explain why the identity of the creator has never been leaked.
Since that first battle between virus and virus destroyer, an ongoing war has been waged between an ever-growing army of viruses and increasingly sophisticated antivirus software. There are so many viruses and other malicious programs lurking in the hidden corners of the Internet that it would be insane to run a computer without proper protection.