Microsoft has confirmed it has bought the office social network site Yammer for $1.2bn. The business, which is four years old and has five million users, operates like Facebook for communication within companies. There had been reports the two were talking about a deal but Microsoft only confirmed the plan on Monday. Yammer is used by firms including the motor giant Ford and the business services firm Deloitte. Microsoft hopes the acquisition will make its range of software products more appealing. Last year it bought the communications business Skype and is integrating it into its products, including its Office software which contributed 60% of its profits last year.