A polymorphic virus is a type of encrypted virus that uses a polymorphic (mutation) engine to fetch itself an encryption algorithm which automatically changes its code whenever it passes to different machine. An encrypted virus contains a virus body, a decryption routine and a mutation engine. The polymorphic code mutates besides keeping the original functional code intact. This makes it the most complex and difficult virus to detect and heel. Some examples of polymorphic virus are Natas (also known as SatanBug.Natas), Tequila, One Half and Maltese.
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