Microsoft Office365, Windows Live Hotmail, SkyDrive and other online services have been hit by a two-hour blackout.
Just seven weeks after the worldwide launch of Office365, Microsoft discounted users' bills by 25% after an earlier three-hour service outage on 17 August, according to Winrumors.com.
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Office 365 provides Office 2010, Exchange, SharePoint and Lync all Online as a cloud-based service that incorporates webmail, collaboration and document management.
The lack of services was initially blamed on "DNS issues". But a Microsoft Office365 spokesman later said the interruption in service was due to a power outage, according to Australian reports.
Several universities in Australia which use Microsoft's Live@edu service reported all services were unavailable and Curtin University also said some Office365 accounts were unavailable.
A power outage knocked out electricity to up to five million people in California, Arizona and Mexico, according to Canadian reports.
The outage was thought to be caused by an employee removing a piece of monitoring equipment causing problems at a power substation in southwest Arizona, officials said.