Just as Mark Zuckerberg won a major legal victory against Cameron and Tyler Winklevoss on Monday, the Facebook founder and CEO faces a new ownership threat from a New York man claiming a 50 percent stake in Zuckerberg's social networking site. When the suit was first introduced last summer, it was widely dismissed in tech circles. Paul Ceglia claimed he signed an agreement with Mark Zuckerberg in 2003 that, in exchange for a small investment in Zuckerberg's site "the face book," entitled him to 50 percent of the now-wildly popular social network.

The suit raised doubts for a number of reasons. First, Ceglia waited seven years to file it. Second, Ceglia is a convicted felon charged with fraud in connection with a wood-pellet company and possession of hallucinogenic mushrooms in 1997. Third, it was just kind of preposterous to believe that, at this stage in the game, Zuckerberg could lose control of social networking behemoth now valued at around $55 billion. And fourth, Facebook flatly denied Ceglia's story. The company repeated that claim today in a letter to Bloomberg saying, “This is a fraudulent lawsuit brought by a convicted felon, and we look forward to defending it in court.”

However, yesterday, Ceglia introduced a new batch of emails that support his claim of a 50 percent stake (you can see them here), and his case is building buzz and curiosity. One exchange between Ceglia and Zuckerberg sticks out in particular. To put it in context, Zuckerberg is arguing with Ceglia over the initial terms of their contract in which Ceglia was entitled to a "1% per day" stake in Facebook every day the launch of the social network was delayed. At the time of this exchange, Facebook's launch had been delayed so long that Ceglia was entitled to an 80 percent stake in the site. Zuckerberg was writing Ceglia to say this wasn't fair because a) Zuckerberg had done all the work on it and b) the launch was delayed because Zuckerberg was doing development work on Ceglia's other site StreetFax.com. Here's the crucial exchange:

Zuckerberg:
 
 
Ceglia agrees to the 50/50 ownership agreement:
 
 

People now reading the emails are beginning to take them very seriously. "The emails don't read 'fake,' writes Henry Blodget at Business Insider. Felix Salmon at Reuters agrees. "The emails Facebook says are fake don't seem that way to me." In any event, everyone agrees that, if the emails are fake, it should be easy for Facebook to demonstrate that. "Facebook almost certainly has a forensic analysis of Mark Zuckerberg's hard drives and email boxes from this period, because these drives would have been the same ones analyzed in the Winklevoss lawsuit," writes Blodget. "Perhaps the drives show different versions of the emails in question--or no emails at all."