Below is an expanded summary of the history of viruses from the start to today.

Narrative histories of the early years by Dr. Alan Solomon and Robert M. Slade are available. Below is an expanded summary.

Note: There are endless arguments about the "first" virus. There were a number of malware attacks in the 1970s and some count these among the virus attacks. The description of the malware, however, would indicate these were worms and not viruses by general definition. Just to be complete, however, the questionable entries from the 1970s are included here with the caveat that Computer Knowledge considers virus history to start in 1981.

Pre 1981 Period

In the early 1970s Creeper was found an ARPANET. It was a worm that moved through modems to other systems where it displayed the message "I'M THE CREEPER : CATCH ME IF YOU CAN." A similar program called Reaper followed Creeper. It appeared to attempt to find and delete Creeper. In 1974 malware called Rabbit which multiplied so fast making copies of itself that systems crashed. In 1975 a game written for the UNIVAC 1108 called Pervading Animal. The game asked questions in an attempt to determine what animal the user had thought of. The game, however, attempted to write itself to every writable program file, changing the creation time to be able to determine if it had already written to that file or not. It was never determined if this Trojan-like behavior was intentional or just an unintended bug. In the theoretical arena Jürgen Kraus wrote a master thesis called Selbstreproduktion bei Programmen (Self-reproduction of programs).

Now, on to the modern history.

1981 - The First Virus In The Wild

As described in Robert Slade's history, the first virus in the wild actually predated the experimental work that defined current-day viruses. It was spread on Apple II floppy disks (which contained the operating system) and reputed to have spread from Texas A&M. [Side note: Thanks to a pointer from anti-virus pioneer Fridrik Skulason we know the virus was named Elk Cloner and displayed a little rhyme on the screen:

It will get on all your disks
It will infiltrate your chips
Yes it's Cloner!
It will stick to you like glue
It will modify ram too
Send in the Cloner!

For more info on Elk Cloner see the author's (Richard Skrenta) page at:

http://www.skrenta.com/cloner/

1983 - The First Documented Experimental Virus

Fred Cohen's seminal paper Computer Viruses - Theory and Experiments from 1984 defines a computer virus and describes the experiments he and others performed to prove that the concept of a computer virus was viable. From the paper...

On November 3, 1983, the first virus was conceived of as an experiment to be presented at a weekly seminar on computer security. The concept was first introduced in this seminar by the author, and the name 'virus' was thought of by Len Adleman. After 8 hours of expert work on a heavily loaded VAX 11/750 system running Unix, the first virus was completed and ready for demonstration. Within a week, permission was obtained to perform experiments, and 5 experiments were performed. On November 10, the virus was demonstrated to the security seminar.

1986 - Brain, PC-Write Trojan, & Virdem

The common story is that two brothers from Pakistan (Basit Farooq Alvi and Amjad Farooq Alvi) analyzed the boot sector of a floppy disk and developed a method of infecting it with a virus dubbed "Brain" (the origin is generally accepted but not absolutely). Because it spread widely on the popular MS-DOS PC system this is typically called the first computer virus; even though it was predated by Cohen's experiments and the Apple II virus. That same year the first PC-based Trojan was released in the form of the popular shareware program PC-Write. Some reports say Virdem was also found this year (it was presented to the underground Chaos Computer Club in Germany in December by Ralf Burger according to reports); it is often called the first file virus.