Yahoo’s turmoil has been largely under the surface for the past few months while it moved to consider bids for its core assets. But now the battle for the company’s future has come to a head, with activist investor Starboard moving to replace the entire board of directors.

As Yahoo CEO Marissa Mayer fights to retain control over the company and dictate the terms of its eventual breakup or sale, a familiar name has appeared: Microsoft. According to a report from tech news site Re/code, the software giant has offered behind the scenes to a number of private equity firms that it would be willing to finance some or all of any bid they make for Yahoo’s business.

The fact that Yahoo will be broken into pieces or sold off wholesale isn’t really in doubt at this point. The board finally agreed to start taking official offers in February, after pressure from Starboard and others based on the decline in the company’s stock price YHOO , and now the activist investor has its sights set on a proxy fight.

Starboard says that it has lost confidence in Mayer and the board, and that new management is needed to bring “credibility to a process that has been publicly criticized repeatedly for being too slow, fraught with conflicts of interest and very difficult for highly qualified and motivated strategic and financial buyers to access much-needed diligence information.”

In a very real sense, Yahoo has been a dead man walking for some time, at least as far as the stock market is concerned. Its most valuable assets are the stakes that it owns in the holding company of Chinese e-commerce giant Alibaba and Yahoo Japan, which are together worth about $30 billion. If you do the math, based on Yahoo’s current market capitalization of about $32 billion, that means Yahoo’s actual core businesses are being valued by investors at next to nothing.

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Yahoo is still hoping to get something from the sale of its core assets, however, which is what the auction process is all about. According to a number of reports, the company is hoping to get as much as $10 billion for its search, advertising and editorial operations, although some analysts believe they may only be worth about half that amount.

The idea that Microsoft might be interested in either buying or helping to buy some of Yahoo’s assets isn’t that surprising, given the history between the two companies. Not only does Microsoft help power Yahoo’s search and advertising, but the software giant has tried to acquire Yahoo more than once. The first attempt came in 2008, when CEO Steve Ballmer offered $45 billion for the company, a bid that was rebuffed.

Microsoft really wants to help Yahoo get sold

Microsoft’s second attempt to acquire some of Yahoo’s assets came as part of a group effort in 2011, led by private-equity firm Silver Lake Partners, along with Silicon Valley venture capital firm Andreessen Horowitz. The group made an offer to acquire 10% to 15% of Yahoo, but the deal never went ahead.

Although investors don’t see much value in Yahoo’s search, advertising, email, and other businesses, Microsoft likely wants to make sure that whoever owns them would make a good partner, since it is already involved in those parts of the company. And if the price was right, the software company would probably be interested in buying parts of Yahoo and adding them to its own similar businesses.

Yahoo may have faded as a competitor, but the website still gets hundreds of millions of visitors, and the company’s email and other services have tens of millions of regular users and subscribers who would be a valuable addition to a company like Microsoft or AOL. Yahoo also has a mobile advertising business that could be worth something. Telecom conglomerates like AT&T and Verizon (which owns AOL) are said to be interested bidders for some or all of the company.