Microsoft may be close to announcing a deal to pay more than $1 billion to buy Yammer, a social network used by more than 200,000 companies, according to a report by Bloomberg News tonight, citing two anonymous people familiar with the matter.

Neither company is commenting on the report, but Bloomberg says it could be finalized by Friday.

The news originally leaked in a very low-tech way, when Sarah Taylor, an administrative manager at Ignition Talent Group, overheard people talking about Microsoft buying Yammer at a coffee shop across from Yammer’s San Francisco office.

She tweeted about what she heard, Business Insider’s Owen Thomas posted about her tweet, and Bloomberg’s sources told the news service that Microsoft is, in fact, in negotiations to buy the company.

Yammer offers a Facebook-style interface used for communication and collaboration inside companies. Its customers include Vodacom, Ford Motor Co., LG Electronics and many others. Apart from continuing to offer Yammer on a standalone basis, Microsoft could potentially incorporate the technology more tightly into its SharePoint software, building on work that Yammer has already done to work with the Microsoft enterprise collaboration platform.

A deal, if it happens, would be part of a wave of consolidation in business-oriented social media. Salesforce.com and Oracle have made acquisitions of their own in this area.

Aaron Levie, the CEO of file-sharing company Box.net, writes on Twitter, “Microsoft buying Yammer would be their best strategic move since launching MS-DOS.”

Microsoft’s largest acquisition to date was also an online communications company, Skype, purchased for $8.5 billion.

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