One in five has illegal copy of Windows

Microsoft's Genuine Advantage programme has seen more than 500 million users validate their copies of the Windows XP operating system, the company has revealed.

However, of those users, over 100 million were found to be using pirated copies of Windows XP. The scheme is designed to sniff out illegal copies by matching codes inside the operating system with codes known to be used by software pirates.

If a user is found to have an illegal copy, they are unable to download updates from Microsoft, and are shown a 'nag-screen' before being able to start Windows. However, the company is not taking direct action against such people.

They are given an option to upgrade to a paid-for version, or can turn in the dealer who sold them the illegal software. Some 56,000 such reports have been made. If users can provide proof of purchase and details of the dealer, they may be entitled to a free upgrade to a genuine copy of Windows.

Of the 512 million people who tested their computers, some 114 million non-genuine installations were found - a rate of just over 22 per cent.