High street retailers are selling PCs that are not protected against the Blaster virus, causing havoc for consumers.
The problem centres mainly on PCs which were manufactured and installed with Windows XP or Windows 2000 before Microsoft released the patch for this virus in July.
But although major retailers such as PC World, Dixons and Comet are aware of the situation, there are likely to be hundreds of vulnerable machines still in retail outlets around the country.
vnunet.com has learned that a number of people who bought PCs in the past few weeks from some high street stores logged onto the internet only to become infected almost immediately.
Mrs Jane Wilson at first thought the virus was already installed on the new PC she had bought.
"I had just bought a Cybercom PC from Staples and on setting it up it was found to have the MSBlaster virus," she told vnunet.com.
"This happened when I logged on to the internet. Luckily, my brother was available to come and get a patch and get rid of the virus.
"I would like to warn readers that there is a possibility of new PCs having a virus. Had I been on my own when I set the computer up I wouldn't have had a clue what to do."
To ensure that customers do not fall foul of MSBlaster, many retailers are now warning customers of the problem, giving them advice on how to protect themselves.
A spokeswoman for PC World told vnunet.com: "We manufacture Advent PCs and, when the situation became known, we recalled many PCs to install the patches,"
"But we also sell other brand names and for these, and our own PCs already in-store, we are giving advice at point of sale and a free CD-Rom with the patch even if we believe the computer has been patched. So customers can use this instead of going online to download the patch."
Customers buying build-to-order PCs from manufacturers such as Dell and Mesh are unlikely to be at risk, because they were alerted by Microsoft and able to install the updated version of XP at source before dispatching orders.
A Dell spokesman said: "We keep no stock; nothing that hasn't just been built. When we pre-install XP we use every update as soon as we learn of the situation."
Buyers of new PCs unsure of whether their computer is patched should go straight to Microsoft's security website here.
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