Microsoft Corp. is buying Yammer, a social networking service for businesses, for $1.2 billion, the companies announced Monday.

Attorneys from Orrick, Herrington & Sutcliffe in San Francisco, Los Angeles and Menlo Park are representing S.F.-based Yammer in the all-cash deal. M&A partner Richard Smith in San Francisco and corporate partner Daniel Friedland in Los Angeles led the Orrick team.