Gate io, a US based crypto exchange with a daily trading volume of $94 million, said it has lost over 40 000 Ethereum Classic worth over 220 000 USD after a hacker attack on January 7th. It is assumed that it was a “51%” attack, in which a user or a group seizes the control of the majority of mining power to monopolize control over the network. A successful “51%” attack will allow hackers to rewrite the transaction history of the block chain and double spend coins for fiat currency. Such kind of attacks are typical for block chains that use a proof-of-work (PoW) algorithm. “It happened between 0:40 Jan.7, 2019 and Jan 4:20 Jan.7, 2019 UTC for about 4 hours. All the transactions were confirmed normally on the ETC blockchain and became invalid after the blockchain rollback”, Gate io announced.