Mining pool, Etherchain, has reported that Ethereum Classic (ETC) has succumbed to a successful 51% attack “with multiple 100+ block reorganization.”
A 51% attack occurs when a malicious actor commands more than half the hashing power on a blockchain. It allows the attackers to “double spend” a cryptocurrency, hence why it’s often known as a “double spend attack.”
“Block reorganization” as mentioned in Etherchain’s tweet, refers to a blockchain which excludes blocks that were initially thought to be part of the longest chain. This is consistent with a double spend attack.
We can confirm that there was a successful 51% attack on the Ethereum Classic (#ETC) network with multiple 100+ block reorganization. We recommend all services to closely monitored the chain and significantly increase required confirmations.
— Bitfly (@etherchain_org) January 7, 2019
Rumors of a 51% on the ETC blockchain emerged early on January 7th. The Ethereum Classic Twitter account initially dismissed the rumors. However, they have since recognized the attack and advised all exchanges and mining pools to increase confirmation times.
Ethereum Classic forked from Ethereum after the community’s controversial decision to reverse a hack in 2016.
Block Explorer will update this article as we learn more.
Further reading: What is a 51% Attack?