A worker prepares the logo on the Microsoft stand on the CeBIT computer fair in Hanover. Credit: Reuters/Tobias Schwarz
According to the Telegraph, the site is currently used by over 200,000 companies, including Ford and eBay.
Unlike Twitter, which is used for broadcasting messages to the public, Yammer is used for private communication within companies.
The social network operates as a freemium service, offering a basic free service, as well as a premium version of the service for five dollars per user per month.
Meanwhile, Frank Shaw, a spokesman for Microsoft, has declined to comment on the latest report.