The word Trojan is derived from the ancient Trojans wars in which the Greeks gifted a wooden horse to their enemies, the Trojans.

In the world of computers the role and procedure of a Trojan is not much different.

A Trojan is a malicious program that has been embedded inside a legitimate and useful software.

Trojans are primarily used to gain back door access to a computer.

Trojans are also used by hackers to remotely control a computer. Once the Trojan had been deployed to a user's computer the hacker can use that computer as a bot to prepare a much large scale and massive attack on targets like servers or websites.

The hacker can steal data, store malicious files, deploy spying tools, watch the user screen and crash the users computer using a Trojan. The hacker can also use the Trojan to use a user’s computer as a proxy to do illegal tasks, users having older versions of internet explorer or Google chrome are vulnerable for such an attack due to security lapses.

A Trojan must not be mixed with a virus, it is not a virus since it do not replicates itself nor it spreads to other computers like viruses do, but it is even more harmful for a computer than a virus and special arrangements must be made to secure computers from Trojans.

There are different kinds of Trojans like :
•    Remote Access Trojans
•    Password Stealing Trojans
•    Keylogging Trojans
•    Proxy Trojans
•    DoS attack Trojans
•    FTP Trojans
•    Software detection killers

A Trojan can be programmed to perform a single of the above mentioned tasks or a single Trojan can be developed to perform all of the aforementioned tasks. It depends on the level of sophistication , functionality and complexity of the Trojan.