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Last Updated: Tuesday, 4 May, 2004, 10:20 GMT 11:20 UK
Q&A: The Sasser worm
The Sasser worm is the latest headache for Windows users. But what is it, how dangerous is it and what can you do about it?

Windows XP on sale, PA
Unpatched versions of Windows XP are vulnerable
What is the Sasser worm?

Sasser is a program that takes advantage of a hole in Microsoft's Windows. It is different from a virus which often travels by e-mail and relies on you clicking on an attachment.

This is a worm which means it can spread by itself, without human intervention. So you could be infected by just connecting to the internet. But the worm only affects computers running recent versions of Windows XP and Windows 2000.

What damage does it do?

The worm causes some computers to continually crash and reboot, but it does not appear to cause any permanent damage to files or machines. Infected computers then also send out the worm, looking for more victims.

So far four variants of Sasser have been spotted on the internet. The latest version, Sasser.D, scans so aggressively for new computers to infect that it may cause networks to become congested with packets of data and slow down.

How widespread is the Sasser worm?

Some security experts estimate that more than one million computers have been infected. Disruptions in at least seven large companies across the world have been blamed on machines infected by Sasser. Post offices have been affected in Taiwan, hospitals in Hong Kong, and banks in Australia.

What can I do about it?

Microsoft and many security firms have released software tools that can help you find out if they are infected and to help them remove the virus from their system. A good place to start is Microsoft's own security advice page at www.microsoft.com/security/.

You should keep your Windows software up to date by regularly downloading the latest patches for free from Microsoft at windowsupdate.microsoft.com/.

Computer users are also advised to install anti-virus software and keep it up to date. If you have a broadband connection use a personal firewall to close the backdoors that some malicious programs install on your PC.

Windows XP comes with a built-in firewall but it needs to be switched on. Various firewall products are available commercially and some are free for personal use.

The BBC's Kevin Anderson
"Computers only need to be switched on and online to become infected"

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