Metamorphic malware [1]. Metamorphic code is used by computer viruses to avoid the pattern recognition of anti-virus software. [2]

> A metamorphic virus is a type of malware that is capable of changing its code and signature patterns with each iteration. [1]

[1] https://www.techtarget.com/searchsecurity/definition/Metamor...

[2] https://en.wikipedia.org/wiki/Metamorphic_code