Mt. Gox, once the worlds largest bitcoin exchange, has been sued by a customer in what may be the first of many U.S. lawsuits seeking to recoup millions of dollars of losses linked to a hacking attack that led to the exchanges bankruptcy. In a complaint filed on Thursday in U.S. District Court in Chicago, plaintiff Gregory Greene said Mt. Gox and its chief executive, Mark Karpeles, were negligent and committed fraud for having failed to protect the Tokyo-based exchange from theft. Greene said bitcoin prices plummeted after Mt. Gox found the security breach, but said he and other investors in the virtual currency could not cut their losses because the exchange had halted trading. Mt. Gox took down its website on Tuesday.