Late last night we started receiving reports from readers experiencing problems with Windows Genuine Advantage authentication. Users of both Windows XP and Windows Vista were writing to say that they could not validate their installations using WGA, and one user even said that his installation was invalidated by the service.

We contacted our sources at Microsoft, who told us off the record that the company is aware of a major WGA server outage affecting users across the globe. The Windows Genuine Advantage support forum has exploded with complaints as a result, and Phil Liu, WGA project manager, says that he won't sleep until the problem is fixed. Windows Vista and XP are affected, 32- and 64-bit versions.

Microsoft is telling users who are affected that they should "try again" later, with some support techs telling readers that Microsoft is aiming to have a fix in place by Tuesday, August 28. That would mean the outage will last more than three days, given that it started last night (and may have started earlier; we're hearing reports of some users running into this earlier in the week, on a limited basis).

Reader Aaron Woolf tells us he was unable to validate patches for installation on a developer's copy of Vista pulled from MSDN. He writes, "My legitimate MSDN-acquired Vista Ultimate, which has been running, activated and validated for several months, now fails WGA." Others have reported similar difficulties.

How does this affect you?

If you use Windows, do your best to avoid anything that requires a ping to WGA. That means you should stay away from patches and add-ons until the coast is clear. WGA will not reach out across the Internet and deactivate your copy of Windows, but you should avoid talking to a WGA server for any reason.

For those of you doing installations and upgrades this weekend, we recommend that you avoid activation at this time. Remember that you can run Windows legally for 30 days without activating.

If you attempt a validation and it fails, your install may be marked as non-genuine, which could lead to several annoyances. First things first, do not reboot a Windows machine that has been marked as non-genuine. Once you do so, you will lose functionality and the Aero interface. It would be best to wait until this problem has been resolved.

The cause

Right now we don't have official word on a cause, but one source familiar with WGA tells us that the issue may be caused by updates to the service that were required after Microsoft expanded the number of activations keys available for Windows XP. However, the sense we get from Phil Liu is that Microsoft is pretty much in the dark right now.

More as this develops...

Update: Word from Microsoft is that this problem has been fixed, and all users affected should revisit the WGA site and re-validate. There's no explanation as to why Microsoft was originally telling people to wait until Tuesday, but the good news is that the problem has been solved.