Microsoft is expanding its Windows Genuine Advantage (WGA) programme that tells business and consumer XP users whether they are running a legitimate copy of the software. It will also extend some aspects of the scheme to Microsoft Office for the first time.

From today, connected users running an unlicensed version of XP will be notified through Windows Update. They will then be asked to validate their PC by purchasing legitimate copies at about £53 for the Home version and £92 for the Pro version.

Users who do not validate their software will continue to receive critical security updates but deeper cover through programs such as the Windows Defender anti-spyware tool and Internet Explorer 7.0 browser with new security features will not be offered as free downloads. They will also suffer recurring pop-up reminders that their software is invalid.

“We don’t want to open up an opportunity to hackers by leaving users without critical security but they will lack better defences,” said Michala Alexander, head of anti-piracy at Microsoft UK.

The WGA programme was launched in July 2005 but this is the first time UK users have not had to opt in to the scheme.

Users who acquired pirated software unknowingly will still be able to claim a free upgrade if they can convince Microsoft of their innocence, although Alexander said few users had pursued this line.

Microsoft is also extending part of the scheme through a “soft launch” of Office Genuine Advantage for Office 2003. Unlike WGA this scheme will not have any sweeteners such as additional software, however.

Alexander said Microsoft had no plans to extend the Genuine Advantage schemes to older versions of Windows or Office or to other programs. Neither does it plan to pursue individuals who have invalid copies despite having a “zero-tolerance” attitude to resellers distributing invalid software.

Microsoft cited Business Software Alliance data that suggests 27 percent of software applications running in Britain are illegal versions.