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Pete Roythorne gets to grips with viruses

Rarely a day goes by when we're not warned about another virus set to make our computers grind to a standstill. But do you know your worms from your Trojan horses, or your logic bombs from your spyware?

The term virus is often used as a catchall for all these, but we should really use the term malware, the generic term for software designed to infiltrate or damage a computer system.

While a virus is a self-replicating program that spreads by attaching itself to a program and infecting PCs, a worm, although also self-replicating, is self-contained and does not need to be part of another program to spread itself. Well-known examples include email-born attachments such as the Mellissa, Sobig.F and I Love You worms.

A Trojan horse, like its namesake in Greek mythology, is a malicious program disguised as legitimate software. It may look useful, but will attack your computer when you run it.

Spyware is software that surreptitiously monitors the user, and has also come to refer to software that subverts the computer's operation for the benefit of a third-party, such as in delivering unsolicited pop-up advertisements, theft of personal information or monitoring web-browsing for marketing purposes.

Some viruses have a delayed effect; these are referred to as bombs. A time bomb strikes on a particular date or time, and a logic bomb occurs when the user performs a task that triggers the bomb. There are also macro viruses which are written in the scripting language in Microsoft programs such as Word and Excel, and are spread via infected documents.

Avoiding viruses is as much common sense as anything: regularly upgrade your anti-virus software, install a firewall (software that acts a barrier between you and the outside world), avoid pirate software and never download an email with an attachment you're not expecting.

Alternatively, buy a Mac! Although many argue that PC viruses outnumber Mac viruses because of the proliferation of PCs, making it unattractive to digital criminals, Macs are accepted by most experts as being harder to penetrate: 60,000 Windows viruses v 40 or so Mac Viruses.

But don't get complacent, thousands of new viruses were written in the last six months. And their writers are getting more and more creative!


You can download free Anti-virus software from

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