[Updated with more info from Microsoft and Google.]

Microsoft’s Live@edu service has surpassed 22 million users, growing more than 100 percent over the past year, making it the most widely used cloud productivity service for education, the company said this morning.

The free cloud-based email, storage and collaboration service competes with Google Apps for Education, which says more than 60 of the top 100 schools are using its service. A Google spokesman notes that 15 million students, faculty and staff using Google Apps for Education.

Google compiles its numbers based on active users (people who have used their accounts in the past 30 days). We’ve asked Microsoft for more information on how its stats are calculated. [Update: Microsoft says the 22 million is active user accounts, but it doesn’t disclose the timeframe for usage.]

Microsoft lists new Live@edu schools including Southern State Community College in Ohio, New Mexico State, Florida State, and the University of Colorado at Boulder in the United States, in addition to more schools internationally.

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