Polymorphic virus is a type of destructive program that can change its appearance with every infection. It is also known as encrypted virus because it uses the encryption technique to hide from antivirus software.
- This virus creates slightly modified, fully functional copies of itself during the process of infection.
- Examples: Chameleon, Cascade, Evil, Phoenix, Proud etc.
Chameleon, regarded as first polymorphic virus became known in the early '90s. But the problem with polymorphic viruses became really serious only a year after that in April 1991.