The second attack was perhaps more important, although smaller in monetary terms ($1.68 million). By striking twice, the attacker proved the blockchain has seemingly no ability to protect itself from meaningful exploits. A 51% attack on a blockchain refers to a miner or a group of miners trying to control more than 50% of a network’s mining power, computing power or hash rate.
Ethereum is a hard fork of Ethereum Classic. The two chains split in 2016 in a disagreement over the value of immutability following a compromised smart contract, The DAO, causing a blockchain “rollback.” At that time, Ethereum Classic developers decided to eat the attack’s losses. The majority of Ethereum’s leadership and hashing power did not and hard forked under the ETH ticker.
Four years later, Ethereum Classic has continued to operate in the shadow of Vitalik Buterin’s Ethereum. The smaller chain’s last few hard forks have all but copy and pasted Ethereum’s work. Yet, the project has differentiated itself on one point: a commitment to the Proof-of-Work (PoW) consensus algorithm used by Bitcoin. Ethereum, on the other hand, has slowly moved toward the novel Proof-of-Stake (PoS) under the Ethereum 2.0 project.
That technical decision is under heightened pressure. PoW coins with low hashing power are liable to being 51% attacked. And Ethereum Classic seems unable to do anything about it for the time being.