Polymorphic Virus - Computer Definition
A virus that can alter its byte pattern when it replicates, thereby avoiding detectioin by simple string-scanning intrusion detection techniques.
Symantec Security Response. Glossary. [Online, July 15, 2004.] Symantec Security Response Website. http://securityresponse.symantec.com/avcenter/refa.html.
A virus that changes its binary signature each time it infects a new file. Using a random number generator, a unique key can be created to encrypt each virus download that self extracts and executes when opened. Without an identifiable pattern to match, the only way to discover a polymorphic virus is by its actions (see behavior detection). See self-extracting file. Also called a "stealth virus," hundreds of thousands of polymorphic Windows viruses are discovered every day. The actual number of antivirus families that generate that many files is perhaps a few thousand. See virus and antivirus program.