South Korea's Upbit, which styles itself as 'the most-trusted crypto-asset exchange', has temporarily frozen withdrawals and deposits after losing $49 million worth of ether in a single transaction.
The exchange confirmed the loss this morning, noting that 342,000 ether has disappeared from its wallets due to an "abnormal transaction" in the early hours of Wednesday morning.
Upbit later posted a support notice saying it had suspended its cypto-asset deposit and withdrawal service due to "server maintenance".
The firm has been busy transferring hot wallets to cold storage to protect user assets.
The company says the suspension will be lifted within two weeks time and that all losses will be reimbursed.