Microsoft suffered a massive server outage yesterday that left users of, Hotmail, Calendar and SkyDrive unable to access all or parts of those services for a 16-hour stretch. In a blog post explaining the situation, Microsoft's Arthur de Haan said the incident occurred after attempting a routine firmware update on its data centers that failed in an unexpected way and resulted in a rapid and substantial temperature spike.

This spike was significant enough that it caused data center safeguards to come in to place for a large number of servers, which is what ultimately caused the downtime. A mix of infrastructure software and "human intervention" was required to bring the servers back online. The company didn't provide numbers for the amount of users affected but it appears the problems weren't widespread.

Even so a 16-hour outage is rather unusual for such a high scale web service. Microsoft said requiring human intervention is not the norm in these situations and that's what added significant time to the restoration, which was finalized by 5:43 AM PDT on March 13. The company also reminded users they can always head to to get real time information specific to any service issues.

This is the second time in roughly two months that Microsoft has experienced server problems, after Office 365 and went down on February 1st for some users in North America.

Although Microsoft's online services have traditionally had good uptime, the latest couple of outages are an ironic twist as Microsoft is currently transitioning its Hotmail user base over to and running a massive marketing campaign for its revamped email service that includes bashing Google's rival Gmail offering.