By Sophie Knight TOKYO (Reuters) – Mt. Gox said on Friday it found 200,000 forgotten bitcoins on March 7, a week after the Tokyo-based digital currency exchange filed for bankruptcy protection, saying it lost nearly all the 850,000 bitcoins it held, worth some $500 million at todays prices. Mt. Gox made the announcement on its website. Online sleuths had noticed around 200,000 bitcoins moving through the crypto-currency exchange after the bankruptcy filing. The exchange, headed by 28-year-old Frenchman Mark Karpeles, said the bitcoins were found in an old-format online wallet which it had thought no longer held any bitcoins, but which it checked again after its bankruptcy filing.