ALSO CALLED: Malicious Threats, Malicious Computer Code, Malicious Logic, Joke Programs, Blended Threats, Malicious Software, Malicious Code, and Mobile Malware
DEFINITION: Polymorphic malware is harmful, destructive or intrusive computer software such as a virus, worm, Trojan or spyware that constantly changes ("morphs"), making it difficult to detect with anti-malware programs. Evolution of the malicious code can occur in a variety of ways such as filename changes, compression  … 
Definition continues below.

MALWARE DEFINITION (continued): …  and encryption with variable keys.

Although the appearance of the code in polymorphic malware varies with each "mutation," the essential function usually remains the same. For example, a spyware program intended to act as a keylogger will continue to perform that function even though its signature changes. If the malicious program is discovered by an anti-malware vendor and its signature is added to a downloadable database, the anti-malware program will fail to detect the rogue code after the signature has changed, just as if a new … 
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