Microsoft buys social network Yammer for $1.2bn The deal represents Microsoft's latest attempt to adapt to a major shift in the technology industry. Microsoft already owns a range of business products. Adding Yammer would step up the rivalry with Salesforce.com, which landed social-marketing tools when it paid $745m purchase for Buddy Media earlier this month. Yammer operates as a 'freemium' service, offering a basic free service, as well as a premium version of the service for $5 per user, per month. Last year, Microsoft bought Internet video chat service Skype for $8.5bn in the biggest acquisition in the company's 37-year history.