Chameleon (early 1990) –is the first polymorphic virus. Its author, Mark Washburn, took data from the Vienna virus from Ralph Brueger's ‘’Computer Viruses: The Disease of High-Tech’’ book, and added to them the advanced principles of Cascade virus self-encoding (the ability to modify both the virus and the decoder external data) used by the Chameleon virus to create.

This technology was quickly adopted and, in combination with technologies (Stealth) and (Armored), allowed new viruses to successfully counter existing anti-virus packages. With the advent of this technology, the fight against viruses has become much more difficult.