The troubled MtGox bitcoin exchange filed for bankruptcy protection in Japan Friday after claims of a multi-million dollar theft from its digital vaults, media reports said. The Tokyo District Court accepted the application from MtGox, Jiji Press and public broadcaster NHK said. The action was taken after US prosecutors reportedly served a subpoena on the company. The website of Tokyo-based MtGox went dark on Tuesday, possibly heralding huge losses for investors, and sending ripples of alarm throughout the global community of digital currency adopters. MtGox froze withdrawals earlier this month, claiming there was a bug in the software that underpins Bitcoin, making it vulnerable to thieves. The value of the volatile unit plunged on the Tokyo exchange and was hovering around $130 on Tuesday, just quarter of what it was fetching on other platforms, until the site suddenly disappeared at lunchtime.