What are Trojans (a.k.a. Trojan horses)?

In short, Trojans are malicious programs that pretend to be legitimate tools, but are designed to perform additional, usually malicious, tasks. There are two common forms of Trojan horses. One is a standalone program designed to act as a Trojan. The second form is a corrupted legitimate program that has been modified by a hacker to perform some additional tasks. Such modification is usually relatively simple and involves downloading and installing a full-scale backdoor in the system.

Unlike worms and viruses, Trojans do not install themselves automatically. Instead, they try to convince the user to install them, pretending to be some useful software tool, a game or a security product (like many of the infamous rogue anti-spyware programs). After activation, they usually pretend to either be inactive or they seem to work just like the user expects, all the while they are modifying your system.

The critical point in Trojan infection is downloading and opening the Trojan horse. The best way to prevent the Trojan threat is to never open unknown files and never download anything from ill-reputed sites.

The threat range

There are many different types of Trojans and they vary depending on the task they perform. Keep in mind that many Trojan horses have two or three main features. Trojans represent a serious threat to your system security as they may perform the following malicious actions:

*personal data thefts,

*creating a backdoor remote controller, giving hackers the total control over your PC,

*creating a stealthy proxy server and using it during hacking to mask the true whereabouts of an offender,

*destruction or alteration of data stored on the computer,

*disabling security software present on the PC at the moment of Trojan installation.

All Trojans are inherently dangerous and should be removed as soon as they are detected. There is simply no limit to the harm they can cause if we leave them alone.


While the danger represented by Trojan horses is real, we can easily protect ourselves from Trojans by applying the following simple security rules:

*never open email attachments from unknown sources and confirm that the attached files in emails from your friends are legitimate

*avoid using P2P networks like Kazaa and BitTorrent to download executable files - the chances of contracting a Trojan horse are very high,

*keep your system up to date. Many Trojan horses use security exploits and will cease to function if you close them with the right patch,

*use a decent anti-spyware tool such as STOPzilla - all good spyware removers are able to deal with Trojans,

*install and run some antivirus software and a firewall - most firewalls are able to block a Trojan horse from sending any data from your PC.

*Learn the sounds your computer makes when it does things. If you're in the other room and you hear your modem connect to the internet, that should be a red flag that you're infected. If your computer is processing large amounts of information and you aren't even sitting at the keyboard, chances are someone else is using your machine from a remote location.

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