What is a Trojan?

It is a harmful piece of software that looks legitimate. Users are typically tricked into loading and executing it on their systems. - Cisco Systems

Remember, the Trojan horse the ancient Greeks had sent to the city of Troy? Well ... this virus is of a similar nature. In simple terms, it portrays itself as genuine content available for download, and then spreads throughout the system.

This type of a virus is Malware, which basically means malicious software. 83% of the malware found on the Internet is Trojan. This virus disguises itself as a particular application or toolbar you would want to download. Once you click on the download option, it will instead download the Trojan on your system.

This virus can then send out important information from your computer to the hacker. Different Trojan Horse viruses perform different functions as mentioned below. Removing a Trojan Horse virus can be done with the help of Antivirus software.

These are the most commonly used Trojan viruses, wherein the attacker can access all files stored in the downloader's system, after the virus has been downloaded. Important information such as credit card details etc., can be accessed.

This type directly affects passwords that are cached on your system. After these passwords are recognized on your system, they are directly sent to another e-mail address. Any new passwords fed into the system while this virus exists will also be transferred.

This type will log the victim's keystrokes and then these log files are sent to the client. It searches of data in the log files with two functions: offline and online. Even in this situation, the data can be sent to a particular e-mail id.

This Trojan virus is capable of deleting all the files on the victim's or downloader's computer. You can also program this virus in such a way that it gets activated on a particular date, at a particular time, and then deletes all the files.

This Trojan virus tries to congest the Internet connection. It does so by producing a lot of Internet traffic on the downloader's server or his/her computer. It also performs another function―as an e-mail virus―wherein it tries to pass onto many other computers and infect them by attacking a lot many e-mail addresses.

These Trojans change the downloader's computer to a Proxy/Wingate server. After this, the entire world can acquire access to many websites anonymously. Using information the client can then register many other sites and that too, without even being traced.

These are the most outdated and simple Trojan viruses. They perform only one action and that is to open or start a port numbered 21. This is the port for FTP transfers. Any computer can then connect to yours through FTP protocol. Since the more advanced versions are protected through passwords, the only computer that can connect to yours is that of the client or attacker.

These Trojans get rid of the famous firewall or antivirus software programs. After this, the programs can no longer protect your computer and thus the attacker can get complete access to your computer.

As we have learned, we need to be careful with the Trojan virus. Not only because of its deceiving nature, but also because of the harm it can cause.