Types of Trojan Computer Viruses
A Trojan horse is a type of computer virus (a malicious program) that disguises itself as useful software (or a software update) available for download on a users computer. A Trojan virus has two parts: client and a server. The client is the virus itself, cleverly disguised to appear as an application, while the server is the person (attacker) behind the client. Once the Trojan virus executes on a users computer, the server can control virtually all aspects of the machine and gain access to key files, documents and personal information.
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Password Sending Trojan
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A password-sending Trojan scans a computer for all cached passwords and sends them back to the server. It has access to all private passwords (online banking, email, forums and messengers) and routinely sends them forward to the server. Password sending Trojans track keystoke activities and maintain detailed logs of all passwords punched in. An example of a password sending Trojan was the Badtrans.B email virus that was released in December 2001.
Denial of Service (DoS) Attack Trojans
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A DoS attack Trojan is a virus that attacks multiple computers over a network (a local area network or a wider area network) and directs traffic to a single server--flooding it and causing it to eventually cave in under heavy congestion. Infected computers are unable to connect to the Internet or download data. Two DoS Trojans that commonly affect Windows based computers are the RFpoison and W32/Trinoo. The mail-bomb Trojan is a virus that infects multiple computers and email addresses with hundreds of randomly-generated (and nonsensical) subjects, eventually bringing down an email server.
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Destructive Trojans
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Destructive Trojans, like their name implies, infect a computer and delete essential files and folders (for instance exe executable files, ini configuration files and dynamic link library or dll files). Many of them are programmed to automatically delete key system files (without which an operating system is unable to function effectively). Destructive Trojans are either controlled by a back-end server or programmed to strike on a specific day, at a specific time. Examples of destructive Trojans include the Bugbear virus and the Goner worm. The Bugbear virus (also called Tanatos) was released in 2002 to disable firewalls and anti-virus software on user machines. The Goner worm (released December 2001) specifically targeted and deleted anti-virus software and files.
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References
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