Ethereum Classic (ETC)

Ethereum Classic (ETC) is a proof-of-work smart contract platform that continues the original, unaltered history of the Ethereum blockchain. It exists because a portion of the community rejected the idea that a blockchain's ledger should ever be edited after the fact, adopting the "code is law" philosophy: whatever a smart contract executes is final, even if the outcome was exploited by an attacker.

The split traces back to June 2016, when an attacker drained roughly $60 million worth of ether from The DAO, an early crowdfunded investment contract, by exploiting a reentrancy flaw in its code. Rather than accept the loss, the Ethereum Foundation proposed a hard fork that rewound the ledger to a state before the theft. Most of the network adopted the fork as the new Ethereum, but a minority of miners and node operators kept validating the original, unmodified chain, which became Ethereum Classic.

Because ETC was historically a smaller proof-of-work chain sharing Ethereum's mining algorithm, it became a repeated target for 51% attacks, most notably in January 2019 and again in August 2020, when attackers double-spent millions of dollars in ETC by secretly out-mining and reorganizing the public chain. In response, developers deployed defenses such as Modified Exponential Subjective Scoring and checkpointing via VeriBlock, which anchors ETC's history to Bitcoin's proof-of-work.

Ethereum's 2022 move to proof-of-stake ironically strengthened ETC's security: displaced Ethash miners redirected hardware to Ethereum Classic, sharply raising its hashrate and making it the largest proof-of-work smart contract network still in operation today.