Facebook demanded that a New York man who claims he is entitled to 50 percent of the social network immediately produce the purported contract and emails on which he is basing his case.
Facebook last week dismissed the contract as a forgery and in their latest court filing, lawyers for Facebook co-founder Mark Zuckerberg went on the offensive against the man who has filed the ownership lawsuit.
Paul Ceglia, of Wellsville, New York, is a "convicted felon and well-known scam artist who has spent the last decade of his life ripping people off," they said. "The contract is a cut-and-paste job, the emails are complete fabrications, and this entire lawsuit is a fraud."
Zuckerberg's lawyers asked the US District Court in Buffalo, New York, to order Ceglia to produce an original version of the contract and the emails and to allow for inspection of all of his computers.
In a suit filed in June of last year, Ceglia claimed that he signed a contract with Zuckerberg in April 2003 to design a website called The Face Book or The Page Book.
Ceglia's lawyers have produced copies of emails and a contract purportedly signed by Zuckerberg, who was then a student at Harvard University.
But Facebook lawyers said the contract is fraudulent and "Zuckerberg has now declared under oath that he did not sign the contract attached to Ceglia's complaint, and that he did not write or receive any of the purported emails."
Facebook said Zuckerberg had done some work for Ceglia in 2003 on a site called StreetFax.com, which provided a photo database of traffic intersections for insurance adjusters.
"Zuckerberg and Ceglia never discussed Facebook and they never signed a contract concerning Facebook - a fact that is not surprising given that Zuckerberg did not even conceive of Facebook until long after the purported contract was signed in April 2003," they said.
"Ceglia appears to have doctored the genuine contract - which concerns StreetFax and StreetFax alone - and then fabricated emails to make it appear that he and Zuckerberg were actually discussing and reaching agreements about Facebook," they added.
"The fact that Ceglia has spent the past seven years as a hustler engaged in various land swindles and wood-pellet scams further highlights the fraudulent nature of his claims in this case," they said.
New York state Attorney General Andrew Cuomo accused Ceglia in 2009 of taking more than 200,000 dollars from customers of his wood fuel pellet company and then failing to deliver any products or refunds.
Facebook's origins have been the subject of two recent books and a hit Hollywood movie, The Social Network.
A pair of Harvard classmates, Tyler and Cameron Winklevoss, have been involved in a long-running dispute with Zuckerberg over Facebook, claiming he stole their idea for the social network.
The twin brothers agreed to a $65 million settlement but have been seeking to have the case re-examined. A California court this month rejected their bid and the brothers have said they plan to appeal to the US Supreme Court.
Facebook, which launched in 2004, has become the world's most popular social network with more than 500 million members. Zuckerberg's net worth was recently estimated at US$6.9 billion by Forbes magazine.