Near Yammer's office, at the Caltrain station in San Francisco, people were reportedly heard talking about the possible buyout, according to Business Insider. Later, a woman named Sarah Taylor tweeted that she also eavesdropped on people talking about it at The Creamery, a coffee shop near Yammer's office.
That's not all, Business Insider reports that a source inside Yammer has also said that Microsoft is in the works of buying the startup.
Still this rumor is far from being confirmed. CNET contacted Microsoft and Yammer for comment and we'll update the story when we get more information.