Definition: You are given a question on computer security. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: A _________________ may be a hidden part of a program, a separate infected program a Trojan in disguise of an executable or code in the firmware of any system’s hardware.
(A)crypter (B)virus (C)backdoor (D)key-logger

C