Ethical Hacking: Techniques, Tools, and Countermeasures, 4th Edition

Trojans

A Trojan is one of the oldest mechanisms used to compromise computer systems and is still one of the more effective methods of doing so. When planned and implemented correctly, a Trojan can grant access to a system on behalf of the attacker, allowing all sorts of activities to take place.

Software Trojans represent one of the biggest dangers to the end user or owner of a system. Users can be easily coerced into installing or running software that looks legitimate but hides a payload that does something unwanted, such as opening up avenues that an attacker can use. Further complicating matters is the fact that Trojans operate on a principle that can be summed up as “permitting what you cannot deny”—in other words, using ports and mechanisms ...