Ethereum Classic Battered by Two 51% Attacks

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  • Ethereum Classic has suffered a 51% attack for the second time in a week
  • The latest hack has seen 820,000 ETC tokens ($5.8 million) taken
  • Ethereum Classic was 51% attacked in 2019, with 219,500 ETC taken

Ethereum Classic has been battered by two 51% attacks in the space of a week, its third 51% attack in 18 months. The attackers struck twice in quick succession, firstly between July 29 and August 1 and again yesterday, reorganizing thousands of blocks and stealing $5.8 million worth of ETC tokens, causing exchanges such as Binance to stop ETC withdrawals and deposits.

51% Attack Rumors Initially Denied

Rumors of the first attack came on Saturday following a 3,693-block reorganization of the Ethereum Classic blockchain. Initially a 51% attack wasn’t suspected, with developers putting it down to a miner losing his internet connection while mining.

It has since emerged however that an attacker paid about 17.5 ($192,000) on hash rental platform Nicehash to acquire enough hashing power for the 51% attack and managed to double-spend a little over 807,000 ETC. The attackers also received 13,000 ETC as block rewards, taking the total theft to 820,000 ETC tokens worth some $5.8 million.

The destination of the tokens is unconfirmed at this stage, although OKEx or one of its affiliates is thought to be the likely outlet through which the attackers will launder the money.

Ethereum Classic Remains Vulnerable

Ethereum Classic is one of the most vulnerable larger blockchains in the crypto market, with Crypto51 giving it a 107% rate of attack potential through Nicehash. This compares to its sister Ethereum’s 5% Nicehash attack likelihood and Litecoin, Dash, and Zcash, which each have a 4% attack vector.

Ethereum Classic’s vulnerability to 51% attacks has been highlighted in the past, with a prior attack coming in January 2019. That attack saw 219,500 ETC double spent, making this attack almost four times larger in scale. 51% attacks occur when a bad actor controls 51% of the hashing power, giving them the power to reorganize the blockchain and effectively send tokens to themselves.