After issuing notification earlier today, of an imminent
emergency critical patch needed for most versions of the NT core versions of Windows, Microsoft issued a patch for affected systems to Windows Update that resolved the issue this evening.
According to the notification given for the details of the update Microsoft stated: "A security issue has been identified that could allow an authenticated remote attacker to compromise your Microsoft Windows-based system and gain control over it."
Despite the unusual rush to get this patch out, it would be unfair to not give credit where credit is due to Microsoft for taking care of this vulnerability so quickly, albeit without much notice before and after the effect.
Link: For more information, or just run Windows Update.