One in three PCs in the UK is running unlicensed or counterfeit software, putting users at risk of cybercrime, according to Microsoft.

Graham Arthur, anti-piracy attorney for Microsoft UK, said consumers are not aware that counterfeit copies of any developer’s software can be infested with Trojans and other malicious software.

If they are using legitimate but unlicensed copies, he said they get few of the benefits such as support, warranties or certain updates.

Although the problem is not a new one and affects all popular applications, the software giant said in the UK it still takes action each month against more than 10 computer businesses for unlawfully trading its software. In addition, the company takes down nearly 250 items from auction site Ebay every week.

“Many consumers unwittingly buy what they think is genuine software and are not only ripped off but are open to dangers such as computer viruses and identity theft,” said Mr Arthur.

Although piracy levels have been static over a number of years and even dropped very slightly to 26 per cent in 2007 from the 2004 to 2006 levels of 27 per cent, Microsoft said it would not rest on its laurels as it tries to clamp down on the problem.

Currently the most popular pirated Microsoft product is Office 2007. However, Microsoft has admitted that it expects to see the number of counterfeit or unlicensed copies of Windows XP grow as the last legitimate stock finds its way off retailers’ shelves.

The operating system is still hugely popular and many people are reluctant to migrate to Vista.

“Both consumers and genuine computer shops are the innocent victims in the trade of counterfeit and illegal software. There’s still a long way to go if we are to meet our goal of significantly reducing the amount of counterfeit and illegal software currently on offer to our customers,” he said.

One weapon that it hopes will help is its willingness to work with consumers who have unwittingly been sold counterfeit or unlicensed software.

It said it will replace any high-quality counterfeit software free of charge. However, it must not be an obvious fake. Anyone who has bought goods that are noticeably suspect should not expect to be helped, Microsoft said.

Microsoft expects something back in return. If you suspect you have bought fake or unlicensed software you need to tell the company when you bought the software, what it is, how much it cost and from whom you bought it.