A Trojan, short for Trojan horse, is a type of malicious software that misleads users of its true intent.

It disguises itself as a legitimate and useful program, but once executed, it allows unauthorized

access to the user's system. Unlike viruses and worms, Trojans do not replicate themselves but can

be just as destructive. They are often used to create a backdoor to a computer system, allowing an

attacker to gain access to the system or to deliver other malware. Trojans can be used for a variety of

purposes, including stealing information, downloading or uploading files, monitoring the user's

screen and keyboard, and more. The term "Trojan" comes from the Greek story of the wooden horse

that was used to sneak soldiers into the city of Troy, which is analogous to the deceptive nature of

this type of malware in cyber security.

Reference:The EC-Council's Certified Incident Handler (ECIH v3) program covers various types of

malware, including Trojans, in detail, explaining their mechanisms, how they can be identified, and

the steps to take in response to such threats.