Over a 24 hour period between last Friday and Saturday, millions of Microsoft customers who attempted to download software updates from the company's Web site were erroneously accused of running pirated Windows versions, thanks to a glitch in Microsoft's reviled Windows Genuine Advantage (WGA) system. The software giant blamed the error on an unspecified server problem, which has since been fixed.

"Customers who received an incorrect validation response can fix their system by revalidating on our site," says Microsoft WGA senior product manager of WGA Alex Kochis. "After successfully revalidating, any affected system should be rebooted to ensure the genuine-only features are restored."

Users who ran into the issue Friday night and early Saturday morning were predictably upset, with at least one user understandably portraying the issue and Microsoft's silence over that time period as a "disgrace" in Microsoft's support forums. The WGA validation system determines whether the version of Windows XP or Vista you're using is legitimate and not pirated, and prevents users with pirated Windows versions from manually downloading software updates.

This week's problem isn't the first time WGA has betrayed legitimate users, but it's certainly the most widespread. In June 2006, the service was revealed to be secretly "phoning home" to Microsoft's servers without alerting users about the communication, causing some security experts to label WGA as spyware. WGA also suffered from a blackout in October 2006, preventing users from downloading updates.