Microsoft has announced that it will no longer allow illegal copies of its Windows XP operating system to be updated via the web. From today the company has implemented its Windows Genuine Advantage Programme as part of its ongoing anti-piracy campaign.

Users hoping to update their Microsoft software will now have to sign up to the agreement to get downloads. However security updates will still remain available to all Windows users.

Microsoft has also announced that Windows users will no longer be required to enter their 25-digit product key to validate their software as the company has created a system that automatically checks participants' PCs to determine whether they are running genuine Windows software.

On their first visit to the Microsoft Download Center, Windows Update or Microsoft Update, customers will be asked to participate in WGA. They will be prompted to download an ActiveX control that checks the authenticity of their Windows software and, if Windows is validated, stores a special download key on the PC for future verification. The validation process does not collect any information that can be used by Microsoft to identify or contact the user.

The company also says it will replace pirated software with genuine versions - free of charge to customers who submit piracy reports and proof of purchase, and for £61 or £92 for XP Home or Professional editions respectively for customers who submit piracy reports but don't have proofs of purchase.