NEW YORK (MarketWatch) -- A class-action lawsuit has been filed against bitcoin exchange Mt. Gox and its owner, Mark Karpeles, said the law firm that's filed the suit, Edelson PC, on Friday. The firm said the lawsuit was filed in a federal court in Illinois on behalf of all persons in the U.S. whose bitcoins were held by the exchange, and it seeks certification of two classes, the return of user bitcoins and damages against Mt. Gox and Karpeles. A plaintiff named in the suit, Gregory Greene, alleges he alone has lost $25,000 worth of the virtual currency, Edelson added. Mt. Gox has said it was filing for bankruptcy protection and that 750,000 of its customers' bitcoins and 100,000 of its own had been lost.