A malicious code that changes itself with each file it infects is called a:

A.
logic bomb.

B.
stealth virus.

C.
trojan horse.

D.
polymorphic virus.

Explanation:
A polymorphic virus has the capability of changing its own code, enabling it to have many different variants.
Since they have no consistent binary pattern, such viruses are hard to identify.
Incorrect answers:
A:
A logic bomb is code that is hidden in a program or system which will cause something to happen when the
user performs a certain action or when certain conditions are met. A logic bomb, which can be downloaded
along with a corrupted shareware or freeware program, may destroy data, violate system security, or erase the
hard drive.
B:
A stealth virus is a virus that hides itself by intercepting disk access requests. When an antivirus program
tries to read files or boot sectors to find the virus, the stealth virus feeds the antivirus program a clean image of
the file or boot sector.
C:
A trojan horse is a virus program that appears to be useful and harmless but which has harmful side effects
such as destroying data or breaking the security of the system on which it is run.