Answer (C) is correct . Viruses are computer programs that propagate themselves from one computer to another without the user’s knowledge. Trojan horses are voluntarily installed on a computer by the user because they are masquerading as programs the user wants. The Trojan horse contains codes that allow a hacker to later take over the computer or retrieve sensitive data from the computer.
Answer (A) is incorrect because Trojan horses can also corrupt data in certain circumstances.
Answer (B) is incorrect because Trojan horses can also alter programming instructions in certain circumstances.
Answer (D) is incorrect because Trojan horses can also erase executable files in certain circumstances.
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