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Trojans and Worms

Viruses are one example of something known as malware. Malware is malicious software which is designed to damage a computer system without the owner's consent.Trojans and worms are two other types of malware, which are very similar to viruses and often mistakenly classified as viruses.


A Trojan is a virus that hides inside another program. Named after the Trojan horse of Greek mythology, a computer Trojan disguises itself as something else in order to gain access to your computer.

Trojans normally claim to be something useful but are actually malicious. One major difference between Trojans and true viruses is that they do not replicate. Trojans contain malicious code that can cause loss or theft of data. Trojans must be invited onto your computer, eg: by opening an email attachment or downloading and running a file. Trojan.Vundo is an example.
There are two types of Trojan:


Trojans differ from other types of virus in that rather than attaching themselves to existing programs they are complete programs in themselves.

Trojans can be mixed up with the 5 virus types mentioned previously. Where there should be no mix-up, is that viruses and trojans are the same in that they have malicious intent towards users and computer systems.

Click the movie above to see about the threat from trojans and how to minimise the danger.



Worms can replicate themselves from computer to computer without infecting a host program, unlike viruses, which must be carried by a host. Although worms are often carried inside another file, usually a Word document or an Excel spreadsheet, they use the host in a different manner from a virus.

A worm will usually release a document that already has the worm macro inside it. The entire document travels from system to system, so the entire document should be regarded as a worm. W32.Mydoom.AX@mm is an example of a worm. It was designed to allow spammers to send spam e-mail from infected computers.

Like Trojans, worms are self contained programs that are designed to copy themselves from computer to computer. Different worms exploit different weaknesses in the programs that allow computers to communicate with each other.

A common purpose of worms is to install a backdoor into a computer. These are programs that allow others to gain access to your computer.

Johnstone High had a major virus problem in the first two weeks of the summer holidays 2009-2010. The Conficker Worm was found to have threaded its way throught the network, not just in Johnstone High school but in many other parts of the councils's network. This worm brought considerable harm to the network, meaning many machines could not be used for weeks on end.

The video below gives some details on an outbreak of the Conficker Worm earlier in 2009.

Click the movie above to see about the Conficker Worm



Continue to Logic bombs


Examples of anti malware programmes.


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