Of the following virus types, which one changes characteristics as it spreads?

A.
Boot sector

B.
Random generator

C.
Stealth

D.
Polymorphic

Explanation:
Viruses are considered polymorphic if their detection is very difficult or impossible using the virus masks or elements of constants within virus-specific code. This is achieved by encrypting the main code of the virus with a variable keyand random sets of decryption commands, or by executable virus code-changing.