The growing scale of the threat problem

Following the development by Bell Labs in the 1950s of an experimental game in which players used malicious programs to attack each other’s computers, the idea of viruses and worms infecting and spreading across networks was floated in both academic circles and the sci-fi world. However, it took until 1986 for the first recognizable PC virus to emerge: Brain was allegedly written by two brothers in Pakistan, and was activated when booting up from floppy disks.

Recognizing the increasing threat of viruses, the emerging anti-virus industry developed signature files to identify the unique strings of code in known viruses. In response, virus writers began to develop polymorphic viruses which mutated as they spread, making detection and disinfection more difficult. For a brief period, there were also attempts to evade detection by making virus code sequences very short.