MICROSOFT HAS AGREED a deal to acquire the private social network start-up Yammer for $1.2 billion (€0.96bn).

Yammer co-founder and CEO David Sacks, former PayPal COO and founder of Geni.com, said on his company’s official blog yesterday that Microsoft will invest in Yammer’s standalone service, but the team will remain under his direction.

The company provides private and internal social networks for companies. It launched in 2008 and currently has over 5 million corporate users.

“When Adam Pisoni and I started Yammer, we set out to do something big. When most people thought social networking was for kids, we had a vision for how it could change the way we work,” he wrote.

“With the backing of Microsoft, our aim is to massively accelerate our vision to change the way work gets done with software that is built for the enterprise and loved by users.”

Microsoft said in a statement that it plans to “accelerate” Yammer’s adoption alongside “complementary offerings” from Microsoft products such as SharePoint, Office 365, Microsoft Dynamics and Skype, which Microsoft paid $8.5bn for last year.

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

The acquisition is subject to regulatory approval.

The Associated Press notes that investors haven’t reacted strongly to the Microsoft-Yammer announcement: Microsoft stock fell by almost 3 per cent yesterday to close at $29.88.

- Additional reporting by the AP