Microsoft’s Outlook.com email service suffered a massive 16-hour outage Wednesday, which saw users unable to access parts of SkyDrive, Hotmail, and Outlook, too. Microsoft has revealed that it was a result of a mischievous firmware upgrade—which caused “a rapid and substantial temperature spike in the datacenter”. It’s quite an unusual situation for a large-volume, high-profile web service. Indeed, it required more than just a few code tweaks to solve, too: “Based on the failure scenario, there was a mix of infrastructure software and human intervention that was needed to bring the core infrastructure back online. Requiring this kind of human intervention is not the norm for our services and added significant time to the restoration.” Exactly what that human intervention was Microsoft doesn’t reveal.

Read the full story at Gizmodo.