Who would thought that a former online Magic Card market wouldn’t be a safe place to invest your money? The Wall Street Journal reports that Mt. Gox, which until last week had been the world’s largest Bitcoin exchange, has filed for bankruptcy. Mt. Gox admitted on Friday that it had lost around 750,000 of its customers’ Bitcoins along with 100,000 of its own Bitcoins, which the Journal estimates all have a combined worth of $473 million. Mt. Gox, which is an acronym for “Magic: The Gathering Online Exchange,” halted all transactions earlier this week after it apparently discovered that someone had been slowly robbing it of Bitcoins for years. Apparently a hacker figured out a way to withdraw Bitcoins from