A Polymorphic virus produces varied but operational copies of itself in hopes of evading anti-virus software.
The following answers are incorrect:
boot sector. Is incorrect because it is not the best answer. A boot sector virus attacks the boot sector of a drive. It describes the type of attack of the virus and not the characteristics of its composition.
parasitic. Is incorrect because it is not the best answer. A parasitic virus attaches itself to other files but does not change its characteristics.
stealth. Is incorrect because it is not the best answer. A stealth virus attempts to hide changes of the affected files but not itself.