Microsoft launched its Windows XP Counterfeit Project in response to growing volumes of high-quality pirate versions of Windows XP on the market and security concerns about pirated software.
The project will allow businesses to replace up to five copies of fake XP, with legitimate products, subject to strict terms and conditions.
The offer is open to organisations that purchased Microsoft Windows XP Home Edition or Professional Edition Operating System, pre-installed on a new computer before 1 November 2004 in the UK.
If organisations purchased a Windows XP upgrade or the purchase was made under a volume licence agreement then it is not eligible.
Alex Hilton, Microsoft licence compliance manager, said, "This is a great opportunity for users to confirm the authenticity of their Windows XP software, while helping gather vital information about illegal traders."
The initiative was praised by David Frost, director-general of the British Chambers of Commerce.