According to Parity Technologies, an anonymous user managed to gain access to the smart contract in the multi-sig wallet and effectively made himself the owner of the contract in early November. As a result, the Ether in the multi-sig wallets are frozen.
Parity Technologies stated in its blog, 587 wallets is affected but the funds remain in the wallets up to November 13. The frozen amount is 513,774.16 Ether (equivalent to 19 Billions JPY approx.).