The Windows Genuine Advantage (WGA) error that seemed tolock Windows XP and Vista users out of the high-end features of their operating system last week has been blamed on "human error".
Microsoft said the failure shouldn't be called an "outage" since the servers didn't go offline and promised changes have been made to avoid a repeat.
In an earlier statement, the company had downplayed the scope of the problem, saying that fewer than 12,000 systems worldwide had been affected.
In a post to the Windows Genuine Advantage blog, program manager Alex Kochis explained the malfunction of the company's validation servers in the greatest detail so far.
"Nothing more than human error started it all," said Kochis. "Pre-production 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."
Microsoft's anti-counterfeit measures come in two flavours: activation and validation. The former requires users to enter a valid 25-character product key to prove they've paid for a licence; the latter is the term used for all subsequent proof-of-purchase demands, and engages, for instance, before users are allowed to download most software from the company's website.
The problem affected both the activation and validation servers, but while a quick roll-back - within 30 minutes, according to Kochis - solved the activation servers' problems, it failed to reset the validation servers. "We now realise that we didn't have the right monitoring in place to be sure the fixes had the intended effect," he said.
From the timeline he offered up in earlier postings, the failure started on Friday, August 24 about 6:30pm. EDT. It's unclear how long Microsoft was unaware of the problem, although it was presumably measured in hours rather than minutes.