The acquisition by Microsoft comes a little more than a year after it bought popular video-calling service Skype for $8.5 billion. Veteran technology companies like Microsoft and Oracle (NASDAQ:ORCL) have been busy scooping up startups in an effort to better compete with an intensifying competitive marketplace.

They have also been building their enterprise social media portfolios as businesses continue to seek new ways of reaching their target audience. Salesforce.com (NYSE:CRM) earlier this month said it would buy social marketer Buddy Media for $745 million.

The Yammer deal is expected to add to Microsoft's suite of Office products, including Microsoft SharePoint, Office 365, Microsoft Dynamics and other cloud-based business products and services such as Skype.

"The acquisition of Yammer underscores our commitment to deliver technology that businesses need and people love," Microsoft CEO Steve Ballmer said in a statement.