Historical replay · ETC/USD
The Ethereum Classic 51% Attack (January 2019)
In January 2019, an attacker gained majority control of Ethereum Classic's mining power and rewrote transaction history to double-spend coins. ETC fell over 20% as major exchanges halted deposits.
A "51% attack" occurs when a single entity gains control of more than half of a blockchain's total mining (or validating) power, giving it the ability to reverse its own recent transactions — spending the same coins twice — a foundational security assumption most blockchains rely on never actually failing in practice.
In early January 2019, Ethereum Classic — a smaller, less-hashpower-secured fork of Ethereum that continued the original chain after the 2016 DAO hard fork split — suffered exactly this. An attacker briefly controlled a majority of the network's mining power and used it to double-spend an estimated $1 million or more worth of ETC, reorganizing the blockchain to erase and rewrite recent transaction history.
ETC fell from a close near $5.39 on January 6 to an intraday low of $4.13 by January 10 — a decline of roughly 23% — as Coinbase and other major exchanges temporarily halted ETC deposits and withdrawals while investigating the attack, a direct, mechanical consequence of exchanges no longer trusting the chain's transaction finality until the situation was understood.
The event remains a frequently cited case study in blockchain security: it's a direct demonstration of why a blockchain's total hashpower (or, for proof-of-stake chains, total staked value) isn't just a technical statistic but the actual security budget protecting every transaction on it — a smaller, less-secured chain is a genuinely different risk profile than a larger one, regardless of how similar their code otherwise is.