Microsoft's WGA (Windows Genuine Advantage) tool could soon be at the centre of a class-action lawsuit in the US. WGA gathers data on a user's computer in an effort to detect bootlegged copies of its Windows OS (operating system).

The lawsuit, filed in US District Court in Seattle on Monday, alleges the program violates consumer-protection laws in California and Washington state, and laws against spyware, invasive programs that surreptitiously collect data.

Computer users are already sensitised to the question of how they are notified about software installation and privacy issues. Late last year, Sony BMG provoked controversy by shipping 15 million music CDs containing invasive copy protection software that installed itself on buyers' computers.

Sony eventually compensated users who bought the affected CDs, which had software that installed itself without user consent and transmitted data, after a class-action suit.

The suit against Microsoft contends that the company misled users in delivering WGA to computers, masking it under batches of monthly updates that often include critical security patches. It asks Microsoft to delete all data collected by WGA and provide users with the ability to remove the software from their computers, in addition to damages.

"In truth and in fact, Microsoft, in its efforts to maximise revenue through antipiracy measures, misled consumers and the public as to the true nature, functionality and operation of its WGA," the suit said.

Earlier this month, Microsoft admitted a version of WGA under distribution as a 'high-priority' update was in fact a test version of the WGA software. In April, Microsoft stepped up the WGA program, adding a function notifying users if their copy of Windows wasn't valid and causing it to make frequent contact with the company's servers.

In response to user complaints, Microsoft released a new version of WGA this week allowing people to opt out of notifications. The update also changes the frequency with which the program contacts Microsoft to check the validity of Windows.

Users have also complained that the software is buggy, labeling copies of Windows as counterfeits when the licence may have been legitimately transferred to a different piece of hardware.

For computers suspected of running bogus software, Microsoft has blocked downloads of free tools such as Windows Defender, its antispyware tool, but allowed security patches.

Microsoft officials contacted early today did not have an immediate comment.