744,000 BitCoins, until recently worth over $400 million USD, were hacked. As far as I can tell there is no way to get the coins back. One million folks kept accounts, called 'wallets', on the site.
Bitcoins are trading now for US $490 (as of 9:15am), down from over $600 yesterday.
Who stole it? Well, there is a Bitcoin address that recently had BTC782,000 move through it. That address is now empty, but scroll down and see large BTC payments going all over.