The term Trojan horse instantly reminds us of the classical reference of the battle of Troy, but in present context it's more relevant for malicious computer program. Trojan is basically a program that is hidden in the pretext of being a harmless and attractive software download. When downloaded and executed the Trojan programs can harm a computer system in many ways. A computer that is infected by a Trojan virus can be used by another person, mostly hackers and crackers, for sending emails, uploading and downloading files and data copying or destructions.
Trojan horse is spread intentionally by the hackers mainly for using the infected computer for erasing or overwriting data on the computer hard drive, corrupting files, encrypting files of the computer, for uploading and downloading bulk files, logging keystrokes of the user for stealing vital information like passwords of bank accounts and credit card numbers. There are more reasons behind the circulations of Trojan horse virus and they are predominantly wrong business tricks. Trojans can collect email addresses from a computer for spamming. Trojan attacks can also install spyware into the system that keeps track of the user's net behavior a reports data like browsing habits to other people for targeted online marketing.
Trojan horse is also used by the black hat hackers or the crackers for criminal activities. They use Trojan to attack a computer and then phish for bank or other account details that are used for criminal activities like unauthorized fund transfers. Another serious threat posed by the Trojan horses is the execution of the RAT or remote administration tool that lets other user to control the activities of the infected computer. This enables the remote user to use the system for criminal activities, for sending spasm for spreading virus and so on.
As the Trojan horse viruses are hidden in the software downloads you can not really predict the presence of Trojan. Therefore Trojan attacks are so common these days. In most cases the Trojan first disables the anti virus software of the system and hence it is impossible to protect your system from the malicious activities of the Trojan unless you format the hard disc and do a clean installation. But then with so much vital information on the disc it is not always possible to format the system now and then. In this scenario Trojan horse removal software is the best effective solution you have got.