A few years back, Microsoft wanted to buy Facebook for $15 billion. Microsoft CEO Steve Ballmer was really interested, but apparently Facebook CEO mark Zuckerberg said no and the acquisition never happened.

"Yeah, we tried to acquire Facebook," Microsoft M&A executive Fritz Lanman said today at Le Web conference in Paris, according to Seattle PI. "Facebook had a lot of similarities to Microsoft back in the day."

Of course, the deal never went through and Microsoft instead ended up paying $240 million for a 1.6 percent stake in Facebook. Microsoft was criticized for inflating the Facebook value to $15 billion but given that the social networking site is now estimated to be worth at least $50 billion, we'd say it was a smart move. Still, Redmond probably would have rather bought Palo Alto outright.

It's been known for a while now that Microsoft proposed to acquire Facebook, but a Microsoft executive has never admitted the buyout attempt publicly. David Kirkpatrick, author of the book "The Facebook Effect" first described the conversation between the two companies. Here's an excerpt that shows how the story goes:

Microsoft CEO Steve Ballmer had flown to Palo Alto to visit his young counterpart twice. As Zuckerberg is wont to do, he took Ballmer on a long walk. Zuckerberg told Ballmer that Facebook was raising money at a $15 billion valuation. But Ballmer had come with something more sweeping in mind. "Why don't we just buy you for $15 billion?" he replied, according to a very knowledgeable source. Zuckerberg was unmoved even by this offer. "I don't want to sell the company unless I can keep control," said Zuckerberg, as he always did in such situations.

Ballmer took this reply as a sort of challenge. He went back to Microsoft's headquarters and concocted a plan intended to acquire Facebook in stages over a period of years to enable Zuckerberg to keep calling the shots. But Zuckerberg rejected all the overtures. What Ballmer finally agreed to instead was an advertising deal that included a provision for Microsoft to pay a huge amount, $240 million, for a sliver of Facebook, 1.6%. Microsoft's investment gave Facebook an implied value of $15 billion.