How Do Trojan Horses Get on Your Computer?

By Allan Hu

Be careful: Computers are easily infected by Trojans.
i Laptop image by Marek Kosmal from

Trojan horse viruses are files designed to trick computer users into thinking they are legitimate processes. For example, a Trojan might come in the form of a computer game downloaded from a hijacked website. However, the program often does nothing but assist unauthorized access to the host system. Hackers can use Trojans to steal person data, like passwords or credit card numbers. Unlike other computer viruses, Trojans do not replicate themselves.

Game Downloads

Trojan horses commonly infect a system through the facade of free game downloads. This is especially true of illegal downloads shared through peer-to-peer networks.

Email Attachments

Trojan horses can be disguised as legitimate email attachments. A hacker may send thousands of emails that appear to come from a trustworthy organization. The message encourages the recipient to open his attachment.

Web Browser Exploits

Trojan horses can get onto systems through browser vulnerabilities. For example, ActiveX controls are commonly uploaded to hacked websites in order to infect visitors. In most cases, user input is required for this to work. This means downloading and starting a program or plug-in.

Messaging Clients

Hackers may send files via instant messaging programs. The sender may say that a file is a picture of himself or some other legitimate document. The file, when opened, will infect the system with a Trojan horse.

Social Engineering

All Trojan horses are classified as social engineering ploys. In these schemes, users are tricked into believing a malicious program is legitimate. Users must open the files to infect their computers. So be careful with any unsolicited files you receive. Make sure that you have a good Internet security suite active at all times.