August 8, 2010

Trojan Horses: A Self Replicating Virus

Trojan Horse

A Trojan horse, or trojan for short, is a term used to describe malware that appears, to the user, to perform a desirable function but, in fact, facilitates unauthorized access to the user's computer system. The term comes from the Trojan Horse story in Greek mythology. Trojan horses are not self-replicating which distinguishes them from viruses and worms. Additionally, they require interaction with a hacker to fulfil their purpose. The hacker need not be the individual responsible for distributing the Trojan horse. It is possible for hackers to scan computers on a network using a port scanner in the hope of finding one with a Trojan horse installed

For a malicious program to accomplish its goals, it must be able to do so without being shut down, or deleted by the user or administrator of the computer via which it is running. Concealment can also help get the malware installed in the first place. When a malicious program is disguised as something innocuous or desirable, users may be tempted to install it without knowing what it does. This is the technique of the Trojan horse or trojan.

Broadly speaking, a Trojan horse is any program that invites the user to run it, concealing a harmful or malicious payload. The payload may take effect immediately and can lead to many undesirable effects, such as deleting the user's files or further installing malicious or undesirable software. Trojan horses known as droppers are used to start off a worm outbreak, by injecting the worm into users' local networks.

One of the most common ways that spyware is distributed is as a Trojan horse, bundled with a piece of desirable software that the user downloads from the Internet. When the user installs the software, the spyware is installed alongside. Spyware authors who attempt to act in a legal fashion may include an end-user license agreement which states the behavior of the spyware in loose terms, and which the users are unlikely to read or understand.

Purpose of Trojan horses
Trojan horses are designed to allow a hacker remote access to a target computer system. Once a Trojan horse has been installed on a target computer system it is possible for a hacker to access it remotely and perform operations. The operations that a hacker can perform are limited by user privileges on the target computer system and the design of the Trojan horse itself.

Operations which 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 Distributed Denial-of-service (DDoS) attacks)

  • Data Theft (e.g. passwords, security codes, credit card information)

  • Installation of software (including other malware)

  • Downloading of files

  • Uploading of files

  • Deletion of files

  • Modification of files

  • Keystroke logging

  • Viewing the user's screen

  • Software downloads (e.g. A Trojan horse included as part of a software application downloaded from File sharing networks)

  • Websites containing executable content (e.g. A Trojan horse in the form of an ActiveX control)

  • Email attachments

  • Application exploits (Flaws in a web browser, media player, messaging client or other software which can be exploited to allow installation of a Trojan horse)

  • Social Engineering (e.g. A hacker tricking a user into installing a Trojan horse by communicating with them directly)
Additionally, there have been reports of compilers which are themselves Trojan horses. In addition to compiling code to executable form they also insert code into the output executables which cause them to become Trojan horses. This is still distinct from self-replication as the process is not automatic.
List of Worst Trjoan Viruses

  • Melissa

  • Brain

  • Code Red

  • Klez the Conquerer

  • Blaster

  • My Doom

  • Elk Cloner

  • Morris

  • Love Bug

  • LoveLetter

  • Xiongmao Shaoxiang aka Panda burning joss stick

  • A Virtual Card for You

  • SoBig

  • Spyware

  • Sasser

  • Postcard Virus

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