(Reuters) - Microsoft Corp is close to buying business software company Yammer Inc for more than $1 billion, according to a source familiar with the details.

Microsoft's interest in Yammer, known for its social networking functions, could allow the software giant to beef up its offerings for corporations.

A Microsoft spokesman declined to comment. A representative from Yammer did not immediately respond to a request for comment.

Backed by PayPal co-founder and Facebook investor Peter Thiel, Yammer said it counts more than 80 percent of Fortune 500 companies as clients. It raised more than $140 million in venture capital funding.

Bloomberg, which first reported the deal, said the announcement about the transaction was expected at the end of June.

(Reporting By Jennifer Saba; Editing by Marguerita Choy)