1.2. Genesis of Computer Viruses
Virus-like programs appeared on microcomputers in the 1980s. However, two fairly recounted precursors deserve mention here: Creeper from 1971-72 and John Walker's "infective" version of the popular ANIMAL game for UNIVAC15 in 1975.
Even more interestingly, ANIMAL was created on a UNIVAC 1100/42 mainframe computer running under the Univac 1100 series operating system, Exec-8. In January of 1975, John Walker (later founder of Autodesk, Inc. and co-author of AutoCAD) created a general subroutine called PERVADE16, which could be called by any program. When PERVADE was called by ANIMAL, it looked around for all accessible directories and made a copy of its caller program, ANIMAL in this case, to each directory to which the user had access. Programs used to be exchanged relatively slowly, on tapes at the time, but still, within a month, ANIMAL appeared at a number of places.
The first viruses on microcomputers were written on the Apple-II, circa 1982. Rich Skrenta17, who was a ninth-grade student at the time in Pittsburgh, Pennsylvania, wrote "Elk Cloner." He did not think the program would work well, but he coded it nonetheless. His friends found the program quite entertainingunlike his math teacher, whose computer became infected with it. Elk Cloner had a payload that displayed Skrenta's poem after every 50th use of the infected disk when reset was pressed (see Figure 1.8). On every 50th boot, Elk Cloner hooked the reset handler; thus, only pressing reset triggered the payload of the virus.
Figure 1.8. Elk Cloner activates.
Not surprisingly, the friendship of the two ended shortly after the incident. Skrenta also wrote computer games and many useful programs at the time, and he still finds it amazing that he is best known for the "stupidest hack" he ever coded.
In 1982, two researchers at Xerox PARC18 performed other early studies with computer worms. At that time, the term computer virus was not used to describe these programs. In 1984, mathematician Dr. Frederick Cohen19 introduced this term, thereby becoming the "father" of computer viruses with his early studies of them. Cohen introduced computer virus based on the recommendation of his advisor, Professor Leonard Adleman20, who picked the name from science fiction novels.