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Microsoft's servers charged with validating your installs of Windows XP and Vista crashed late Friday night, and for 19 hours, if you needed to validate your install, it informed you that you may have counterfeit software.
Though everything seems fine now, this does reveal a problem with Microsoft's attempts to constantly validate your installs. Every time you download an update or program from the company, it talks to the servers to make sure your copy of Vista is valid: if that service is down, it could say that you are pirate, and in some cases lock you out of your portions of your system.
It is unclear if Microsoft will ever share with the general public what caused the problem, but for now, everything seems to be working okay.