Editing Polymorphic code (section)

== Malicious code ==

Most [[anti-virus software]] and [[intrusion detection system]]s (IDS) attempt to locate malicious code by searching through computer files and data packets sent over a [[computer network]]. If the security software finds patterns that correspond to known computer viruses or worms, it takes appropriate steps to neutralize the threat. Polymorphic algorithms make it difficult for such software to recognize the offending code because it constantly mutates.

Malicious [[programmer]]s have sought to protect their encrypted code from this virus-scanning strategy by rewriting the unencrypted decryption engine (and the resulting encrypted payload) each time the virus or worm is propagated. Anti-virus software uses sophisticated pattern analysis to find underlying patterns within the different mutations of the decryption engine, in hopes of reliably detecting such [[malware]].

Emulation may be used to defeat polymorphic obfuscation by letting the malware demangle itself in a virtual environment before utilizing other methods, such as traditional signature scanning. Such a virtual environment is sometimes called a [[Sandbox (computer security)|sandbox]]. Polymorphism does not protect the virus against such emulation if the decrypted payload remains the same regardless of variation in the decryption algorithm. [[Metamorphic code]] techniques may be used to complicate detection further, as the virus may execute without ever having identifiable code blocks in memory that remains constant from infection to infection.

The first known polymorphic virus was written by Mark Washburn. The virus, called [[1260 (computer virus)|1260]], was written in 1990.<ref>{{Cite web |title=An Example Decryptor of 1260 |url=https://userpages.umbc.edu/~dgorin1/432/example_decryptor.htm |access-date=2025-03-21 |website=userpages.umbc.edu}}</ref> A better-known polymorphic virus was created in 1992 by the hacker [[Dark Avenger]] as a means of avoiding pattern recognition from antivirus software. A common and very virulent polymorphic virus is the file infecter [[Virut]].