THE WINKLEVOSS TWINS have filed details of a new lawsuit against Facebook and its founder Mark Zuckerberg – less than a day after confirming they would not appeal a previous legal defeat against the social network.

The brothers, who claim Zuckerberg stole the concept of Facebook from a similar site they had hired him to work on, are to ask a Boston judge to investigate whether Facebook withheld information from them during talks on a legal settlement in 2008.

Specifically, the Los Angeles Times reports, they want an investigation into whether Facebook “intentionally or inadvertently suppressed evidence” during those discussions, which formed the basis for the Oscar-winning film The Social Network.

PC World says the trio are also looking for access to instant messages sent by Zuckerberg to other people, including Facebook co-founder Eduardo Saverin, which they claim could throw new light on the nature of their business relationship.

If the conversations are released, Cnet added, the three will then seek ‘appropriate relief’.

The Winklevosses had sought to renegotiate that settlement earlier this year, but in April were told they would have to make do with their original $65m deal. Yesterday they said they would not appeal that finding to the Supreme Court.

The Winklevosses – and their original business partner Divya Narendra, who had not sought to appeal the earlier ruling – struck their original settlement based on a share valuation of $36 each.

At the same time, they argue, Facebook was giving staff the option to buy stock for $9 each – meaning Narendra and the Winklevosses could have picked up four times as many shares as they originally got.

The trio say Facebook should have made them aware of the internal stock offerings during the original talks, but that they were never informed of them.

Facebook has dismissed the new claims as “baseless” and that it considered the case to have been “closed for a long time”.

The group’s original project, HarvardConnection, later became ConnectU which closed last year.