Orr
OpenRCE
January 2006
The W32.Evol virus was discovered around July 2000. Its name is derived from a string found in the virus, but much more can be implied from the name. Up until then, most of the viruses were using Polymorphic engines in order to hide themselves from Anti-Virus scanners. The engine would encrypt the virus with a different key on every generation, and would generate a small, variant decryptor that would consist of different operations but remain functionally equivalent. This technique was beginning to wear out as AV scanners would trace virus-decryption until it was decrypted in memory, visible and clear.