BUFFALO, New York: Lawyers for Facebook are calling a man's federal lawsuit claiming part ownership of the company ''a fraud on the court''.

In their latest legal response, the lawyers for Facebook have accused Paul Ceglia of doctoring a 2003 contract that he says proves he bought into the Facebook founder Mark Zuckerberg's idea for the site when Mr Zuckerberg was at university.

Facebook CEO Mark Zuckerberg ... the company says Paul Ceglia's claim of ownership is a "fraud". Credit:AP

Mr Ceglia ''has now come out of the woodwork seeking billions in damages,'' the response filed in the US District Court in Buffalo said.

Mr Ceglia's lawsuit relies on a two-page ''work for hire'' contract.