"Preproduction code was sent to production servers. The production servers had not yet been upgraded with a recent change to enable stronger encryption/decryption of product keys during the activation and validation processes. The result of this is that the production servers declined activation and validation requests that should have passed."
The company stressed that the glitch affected less than 12,000 users and should not be considered an outage, since the servers were never offline. Alex Kochis, senior product manager for Windows Genuine Advantage at Microsoft further clarified that an existing policy will automatically validate all users if the WGA servers are down.
Microsoft said it is implementing some changes to make sure a similar incident doesn't happen again, including new checkpoints that should prevent accidental changes to the servers and improved monitoring in order to find out sooner if there is a problem.