Microsoft officially confirmed that it has sealed a deal to buy Yammer for $1.2 billion in cash. The social networking company offers businesses private social networks to foster communication and interaction among employees; it is used by 85 percent of the Fortune 500 and has attracted 5 million corporate users.

“The acquisition of Yammer underscores our commitment to deliver technology that businesses need and people love,” Microsoft CEO Steve Ballmer said in Monday’s news release. “Yammer adds a best-in-class enterprise social networking service to Microsoft’s growing portfolio of complementary cloud services.”

“When we started Yammer four years ago, we set out to do something big,” said Yammer founder David Sacks. “We had a vision for how social networking could change the way we work. Joining Microsoft will accelerate that vision and give us access to the technologies, expertise and resources we’ll need to scale and innovate.”