Ethereum Classic Undergoes Likely 51% Attack With 3693-Block Chain Reorganization

Ethereum Classic (ETC) suffered a 3,693-block chain reorganization early Saturday morning, an attack first noticed by cryptocurrency miner Bitfly.

• The reorganization caused all state-pruned nodes to stop syncing and is is likely caused by a 51% attack, Bitfly said.
• "Exchanges need to pause [ETC] deposits and withdrawals.", said Hudson Jameson, developer at the Ethereum Foundation.
• Ethereum Classic suffered a 51% attack in January 2019, CoinDesk reported.
• A reorganization happens when two versions of a blockchain compete for validity from nodes in the network. Eventually one chain of blocks will gain a majority of the mining hash power and "win," leaving the competing version to be "orphaned" or abandoned. If the fraudulent chain were to gain the upper hand and "win" it would open the door for invalid transactions could be treated as validated by exchanges and other users.
• So far, the ETC market seems unaffected by the news, having gained more than 1% over the past 24 hours, according to Messari.