Trojan horse

From Saferpedia

A Trojan is a malicious software, malware, unable to auto-multiply an able to trick the users by realizing functions supposed to be desired by user, easing the unauthorized access to the computer. The name was chosen after the "Trojan horse" story from the Greek mythology.

Purpose and operation

Trojans are designed to allow hackers remote access to targeted computers. Once a Trojan is installed on computer there is the possibility for a hacker to remotely access that computer allowing him to realize various actions. Actions a hacker will realize on a computer are as limited as the user he is logged on as.

A hacker will be able to do on a target system:

Use the computer as botnet (to do spam for example);
Data stealing (passwords, credit card information, etc.);
Installing software, including malware;
Downloading or uploading files;
Editing or deleting files;
Overloading computer's memory.

Trojans require interacting with a hacker to achieve its purpose although the hacker doesn't necessarily have to be the responsible person for distributing the Trojan. Actually hackers may scan computers from a network using a ports scan hoping to find a Trojan horse installed, so they can control the target computer.

Installation and Distribution

Trojans can be installed using one of the following methods:

Software downloads (for example a Trojan included into an application);
Sites containing executable files (for example a Trojan as an ActiveX control);
E-mail attachments;
Mining applications (media player, messenger client, etc.)

There were reports regarding the existence of compilers being themselves Trojans.

Removing a Trojan

Antivirus software are designed to detect and delete Trojans and to prevent them installing. Although it is possible to manually delete a Trojan this operation requires an full understanding of its operation mode. If system's security is fully compromised it's recommended deleting all data from the affected hard disk and reinstalling the OS and necessary software.

Current influences

Regarding increasing popularity of botnet among hackers, Trojans become more and more frequent. According to a study realized by BitDefender from January to June 2009 Trojan malware is increasing, representing 83% from global malware.