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.