Microsoft: Overheating caused Outlook and Hotmail shutdown

The new webmail service integrates the firm's Skype video chat functions

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Microsoft has blamed an overheating data centre for a 16-hour shutdown of its Outlook and Hotmail systems.

In a blog post, it said a "rapid and substantial temperature spike" had caused a large number of servers to stop working.

The temperature rise had been due to a firmware update failure, wrote Arthur de Haan, Microsoft vice president.

Microsoft is in the process of migrating millions of Hotmail users to the new Outlook.com service.

The move is seen by some as an attempt to claw back ground lost to competitors such as Google.

"Overall the upgrade has been going very well," said Mr De Haan.

"That said, we had an issue yesterday and wanted to provide you with a deeper look at what happened."

The outage began at 20:35 GMT on 12 March and services were fully restored the following day at 12.43 GMT.

"On the afternoon of the 12th, in one physical region of one of our data centres, we performed our regular process of updating the firmware on a core part of our physical plant," said Mr De Haan.

"This is an update that had been done successfully previously, but failed in this specific instance in an unexpected way."

He confirmed that part of the company's cloud storage system, SkyDrive, had also been affected.

"We sincerely apologise and regret the impact this outage had on all of you," he said.