OKEx

On July 31, 2020, OKEx, a Seychelles-based cryptocurrency exchange, was exploited during a 51% attack on the Ethereum Classic (ETC) blockchain, resulting in the theft of 807,260 ETC (~$5.6 million), as reported by Decrypt. Detected on August 1, 2020, at 12:00 UTC, the attacker, controlling over 51% of ETC’s hash power, created a “shadow chain” starting June 26, manipulating transaction history to redirect funds. Using five KYC-verified accounts, the attacker deposited 68,230 ZEC, traded for 807,260 ETC, withdrew them, then re-deposited and swapped back to 78,900 ZEC on the shadow chain, which recorded the ETC as never returned, per OKEx’s report. OKEx, with $5 billion daily trading volume per CoinMarketCap, blacklisted the attacker’s addresses, suspended the accounts, and planned longer ETC confirmation times, per Twitter (@OKEx). No funds were recovered, and OKEx considered delisting ETC, per the article. The attack, costing the hacker $200,000 to execute, per Bitquery, exploited poor node coordination, per Twitter (@EthereumClassic). One of 208 crypto hacks in 2020 costing $3.7 billion, per Chainalysis, this incident, alongside 2gether’s $1.4 million loss, highlighted blockchain security risks, fueling calls for enhanced confirmation protocols, robust hash power distribution, and improved exchange-node communication to secure crypto platforms.