BY MICHAEL J. DE LA MERCED

Microsoft is officially kicking the tires at Yahoo again, three years after it failed to buy control of the company.

The software giant has signed a confidentiality agreement with Yahoo, according to a person briefed on the move, joining other potential bidders like the private equity firms Silver Lake and TPG Capital. Behind the broad interest in Yahoo is what investors believe is a trove of riches that could be unlocked by providing stronger management. The Yahoo of today is in a weaker position than in 2008, having fallen behind Google and newer Internet players like Facebook. But Yahoo remains a formidable destination, with its news site along attracting 81.2 million unique visitors in August.

By signing the nondisclosure pact, Microsoft will get a closer look at Yahoo’s books. This time around, however, it is unlikely to pursue its own takeover attempt. Instead, it may aid others.

A growing number of parties have signed confidentiality pacts with Yahoo, an indication that there is dwindling resistance to certain requirements of the agreement, including one that prevents potential bidders from talking to each other.

Microsoft held talks with potential partners last month about a possible bid, people with knowledge of the matter have said. Under one such combination, Microsoft would contribute billions of dollars in financing as part of a consortium led by Silver Lake and the Canadian Pension Plan Investment Board. That group would borrow billions of dollars from banks as well.

In that situation, Microsoft would shoulder little operational responsibility for Yahoo, these people have said. These people, and the person with knowledge of the confidentiality agreement, requested anonymity because they were not authorized to discuss private negotiations.

Such a move is radically different from what Microsoft tried in 2008. Then, it offered $45 billion for Yahoo, hoping to create a formidable competitor to Google. Yahoo, led by its co-founder Jerry Yang, rebuffed the effort, setting off a months-long battle that ended with Microsoft walking away.

Since then, the two companies have created a search and advertising partnership, in which Microsoft’s Bing search engine fetches answers to user queries while Yahoo’s sales force sells ads against those results.

Preserving the pact appears to be Microsoft’s primary interest this time around, given that the company receives 12 percent of that advertising revenue.

Microsoft may also push to integrate its newest acquisition, the Internet communications provider Skype, into Yahoo.

Representatives for Microsoft and Yahoo declined to comment. News of Microsoft signing a nondisclosure agreement was first reported by DealReporter.

It is not clear how receptive Yahoo’s board will be to a wholesale takeover effort, however. Others who have signed nondisclosure agreements, like TPG, have considered making only a minority investment in Yahoo, others briefed on those deliberations have said. Such a move would involve Yahoo borrowing money to finance a stock buyback, giving that investor effective control of the company.

Other potential bidders have yet to sign nondisclosure agreements. The Alibaba Group, a Chinese e-commerce company that Yahoo has a 40 percent stake in, has been in talks with private equity firms about making its own bid for Yahoo, people briefed on those talks have said before.

Many possible suitors have approached Alibaba’s chief executive, Jack Ma, to gauge his support for their plans. His support may be important, since Alibaba’s deals with Yahoo give him some say, should Yahoo be sold.

Yahoo’s board is still evaluating potential strategic options with the help of advisers like Allen & Company and Goldman Sachs, and any possible transaction is probably still weeks away.

But the company is under pressure from restive shareholders. Earlier this month, the activist hedge fund manager Daniel S. Loeb publicly demanded two board seats and called upon Mr. Yang to resign.