A Trojan malware
A Trojan horse, or Trojan, is malware that appears to perform a desirable function for the user prior to run or install but instead facilitates unauthorized access of the user's computer system. "It is a harmful piece of software that looks legitimate.A trojan horse is typically separated into two parts – a server and a client. It’s the client that is cleverly disguised as significant software and positioned in peer-to-peer file sharing networks, or unauthorized download websites. Once the client Trojan executes on your computer, the attacker, i.e. the person running the server, has a high level of control over your computer, which can lead to destructive effects depending on the attacker’s purpose.
A horse may modify the user's computer to display advertisements in undesirable places, such as the desktop or in uncontrollable pop-ups, or it may be less notorious, such as installing a toolbar on to the user's Web browser without prior notice. This can create the author of the Trojan revenue, despite it being against the Terms of Service of most major Internet advertising networks, such as Google AdSense.
Trojan horses may allow a hacker remote access to a target computer system. Once a Trojan horse has been installed on a target computer system, a hacker may have access to the computer remotely and perform various operations, limited by user privileges on the target computer system and the design of the Trojan horse.
Operations that could be performed by a hacker on a target computer system include:
* Use of the machine as part of a botnet (e.g. to perform automated spamming or to distribute Denial-of-service attacks)
* Data theft (e.g. retrieving passwords or credit card information)
* Installation of software, including third-party malware
* Downloading or uploading of files on the user's computer
* Modification or deletion of files
* Keystroke logging
* Watching the user's screen
* Crashing the computer
A trojan horse virus can spread in a number of ways. The most common means of infection is through email attachments. The developer of the virus usually uses various spamming techniques in order to distribute the virus to unsuspecting users. Another method used by malware developers to spread their trojan horse viruses is via chat software such as Yahoo Messenger and Skype. Another method used by this virus in order to infect other machines is through sending copies of itself to the people in the address book of a user whose computer has already been infected by the virus.
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