Ethereum Classic Suffers Second 51% Attack In a Week

Published on by Coindesk | Published on

Ethereum Classic has suffered its second 51% attack in a week after more than 4,000 blocks were reorganized Thursday morning.

Mining pool Ethermine's parent entity Bitfly and crypto exchange Binance reported the reorganization, announcing all Ethereum Classic payouts, withdrawals and deposits had been suspended due to the attack.

Developers behind Ethereum Classic said in a tweet minutes before Bitfly's report that exchanges and mining pools are advised to "Significantly raise confirmation times on all deposits and incoming transactions" in light of "Recent network attacks."

This fresh attack to Ethereum Classic's network follows on from a recent attack that occurred between July 29 and August 1, according to blockchain analytics firm Bitquery.

While Ethereum Classic developers initially said the network did not suffer from a reorganization or a 51% attack in that previous attack, Bitquery said Wednesday that an attacker double-spent a little over 800,000 ETC, and paid about 17.5 BTC to acquire the hash power for the attack.

The monetary value of Thursday's 51% attack in terms of the double spends is not yet known.

At $23.44 per block reward on Ethereum Classic, the attacker has most likely earned $93,760 from block rewards alone.

The attack follows the deprecation of the OpenEthereum client on July 16.

The attacker then sent back money to a crypto exchange, which Bitquery alleges belongs to Malta-based OKEx.By August 1 the attacker published their blocks and initiated the chain reorg.

As of press time, none of the funds compromised in the 51% attack have moved from the OKEx exchange, according to Bitquery.