Trojans

These are malicious programs that seem like legitimate software, but actually they when launched, they perform unintended or malicious activities behind the scenes. Most of the remote control spyware programs are of this type. A Trojan program file will look, operate, and appear to be the same size as the compromised system file.

To avoid the effects of such attacks, early use of a cryptographic checksum or binary digital signature procedure is the only protection.