Microsoft on Tuesday released a revamped version of its Windows Genuine Advantage tool that it hopes will reduce complaints arising from paid-up users of Windows XP caught in the dragnet of the controversial anti-piracy program.

The main change in WGA Notifications is a new category of results for PCs with Windows installations of questionable validity.

The change addresses a problem raised by the other half of Microsoft's anti-piracy program, WGA Validation, which was introduced in mid-2005. PCs that were scanned by WGA Validation and failed to prove to Microsoft's satisfaction that they were running non-counterfeit copies of Windows XP were formerly labeled as "non-genuine" by Microsoft.

That caused WGA Validation to disallow access to certain Microsoft software, and WGA Notifications to send periodic messages asking users to reinstall XP or buy a legitimate license for it, leading to "nagware" complaints from some users.

Many users also claimed that WGA, due to technical glitches or other issues, mislabeled their genuine copies of Windows XP as pirated. Microsoft has maintained throughout that the rates of such "false positive" errors were very low.

At the same time, its online forum for WGA-related problems has registered nearly 20,000 postings from aggrieved users.

Tuesday's change in WGA Notifications is aimed at addressing complaints from users who have yet to pass WGA by creating a new "indeterminate" category for copies of XP that failed to prove they were genuine yet did not use a license of XP known by Microsoft to be pirated.

Microsoft keeps a database of pirated XP licenses, most of which are stolen from corporations using a single volume license to install multiple Windows on multiple PCs.

Users with copies of XP labeled "indeterminate" are also provided with more information to troubleshoot the problem, according to a Microsoft spokeswoman.

The majority of Windows XP users, whose copies of XP have already passed Microsoft's WGA program, can safely ignore the updated tool.

Microsoft initially rolled out WGA Notifications this summer as a "critical" fix via Automatic Updates. Many users, calling the program equivalent to spyware, complained they downloaded the pre-release program without their full knowledge. Microsoft subsequently changed WGA Notifications to become an opt-in, normal priority download, a status that does not change with the new version, the spokeswoman said. The program was also shifted out of the testing stage in late June.

Users running copies of XP that Microsoft has already determined to rely on one of four pirated Windows license keys are now being asked to download the revamped tool. That will be gradually expanded over the "next several weeks and months," according to Microsoft, though users will continue to be able to de-select the update from being downloaded and installed.

The new version of WGA Notifications will also not incorporate a "kill switch" that cripples PCs that fail to prove that they are running genuine copies of Windows XP. That more aggressive feature, called Reduced Functionality Mode (RFM), is being introduced in the upcoming Windows Vista OS.

The release also features a new installation wizard and will display validation results as soon as the tool has been installed. The software doesn't need to be rebooted after its installation, Microsoft said.

Microsoft plans to update the tool every 90 to 120 days, as a way to react to re-evaluation of the software and any changes in software piracy.