A law firm has let slip that Facebook paid $US65 million ($A99.04 million) to settle a lawsuit charging that founder Mark Zuckerberg swiped the idea for the website from former college roommates.

Quinn Emanuel Urquhart Oliver & Hedges law firm boasted in a January advertising brochure about outcomes of an array of cases it handled last year, among them a $US65 million settlement from Facebook.

The law firm's ad brags that it is a sound investment and that "it's our opponents who needed a bailout".