"At approximately 11:30 a.m. PDT, Microsoft became aware of a networking issue affecting customers of some Microsoft services hosted out of one of our North American data centers," said Steven Gerri, general manager for Microsoft Global Foundation Services, in a statement

　　"We apologize for the inconvenience that Office 365 outage has caused today. We are working on resolving the issue," the software giant said via Twitter.

　　Outages were reported in Chicago, Denver and New York City among other locations. According to tweets from affected users, they were unable to access their email and managers were unable to manage accounts.

　　The outage lasted approximately five hours and services have been restored for the moment.

　　According to Microsoft service-level agreement, Microsoft guarantees a 99.9 percent level of uptime. If it fails to reach 99.9 percent uptime, users are eligible for 25 percent service credit.

　　As more industry giants try to entice users to move to the "cloud," a term refers to the management and provision of applications and data over the Internet, the downtime again reminds cloud computing users that they must prepare to deal with outages and rethink their dependency on the service, analysts said.

　　Amazon has suffered two major cloud outages earlier this month and back in April, impacting some of its high-profile users like movie streaming service Netflix and location-based social networking Foursquare.

　　Analysts recommend cloud users to store data with multiple service providers to minimize the risk and limit their dependency on cloud services for business-critical processes.

　　Available in 40 countries and regions since June 28, Office 365, which Microsoft CEO Steve Ballmer said is "where Microsoft office meets the cloud," combines Microsoft Office, SharePoint Online, Exchange Online and Lync Online into a single cloud-based package for business users.