Thought I would post this article from Pandasoftware's daily email -

Madrid, November 11, 2003 - The BBC reminds readers -at
http://news.bbc.co.uk/1/hi/technology/3257165.stm -, that this week is the 20th anniversary of the appearance of computer viruses, as dated from the seminal study on this subject published by Fred Cohen in 1983.
Fred Cohen created the first viruses as practical experiments for part of his thesis for a doctorate in Electrical Engineering. In his study, he defined a computer virus as "a program that can 'infect' other programs by modifying them to include a ... version of itself". According to the article published by the BBC, Cohen presented the results of his research to a security seminar on November 10, 1983.
Other origins of computer viruses could date back to the 1950s, when computer pioneer John Von Neumann referred for the first time to self-replicating programs in his essay: "Theory and Organization of Complicates Automata". In those days it was unthinkable to generate a self-replicating program, but Von Neumann set the technical basis for developing such programs by inventing the concept of "stored programs", which made it possible for programs and data to be stored together in memory, and the code to be modified.
A decade later, three researchers at the Bell laboratories created a small game called Core Wars. In this game, two programmers developed applications that fought each other for space in memory. The winner took more memory than its opponent or simply "annihilated" it. Programs tried to survive by using attacking, stealth and replication techniques similar to those used by present day computer viruses. In May 1984, the Scientific American magazine distributed the game Core Wars, which allowed many of its readers to experiment with it.
The official birth of harmful viruses -viruses capable of reproducing and infecting other programs, computers or disks- took place in 1986. These first viruses include Brain, which infected boot sectors of 5.25" floppy disks and the infamous Jerusalem, a.k.a. Friday 13th, the first memory resident virus. This virus went into action on Friday 13th and deleted infected files.