It's been no secret that Microsoft is looking to sell its digital advertising agency Razorfish. But now The Wall Street Journal has more details on the behind-the-scenes talks. It reports that the software giant is in discussions with five giant ad companies -- not only to buy Razorfish, but also to utilize Microsoft ad technologies and purchase "hundreds of millions of dollars" of ad space across its Web properties.

That could make Razorfish -- whose clients include Travelchannel.com, Levi Strauss and Starwood Hotels -- an interesting playing card in Microsoft's pursuit of Google in the online advertising arena.

As previously reported by The Financial Times, Microsoft has tapped Morgan Stanley to assist with a sale. Potential buyers include WPP, Omnicom, Publicis Groupe, Interpublic Group and Dentsu.

The Journal reports that any of those ad companies would need to tread carefully if they were to enter a deep partnership with Microsoft. Reporter Emily Steel writes:

Aligning too closely with Microsoft could pose a threat to a big advertising company's status as a neutral third party supposed to seek out the best deals for marketers. The winning bidder could have a conflict of interest when choosing between search engines to buy ad time on, for instance.

Still, there's a lot at stake with the Journal reporting that Razorfish -- which is based in Seattle and employs 2,000 people worldwide -- could fetch as little as $400 million to several hundred million dollars based on the other advertising elements of the deal. (The Financial Times previously reported that Razorfish could sell for $600 million to $700 million.)

Microsoft acquired Razorfish as part of its $6 billion acquisition of aQuantive.