Ethereum Classic was potentially hit by a double spend attack, but the exact details are still unclear. Here is what is known.
Ethereum Classic’s Twitter posted that “One Private Mining Pool’s Hashrate Hits over 50% of the Entire Network Hashrate.” It was questioned if this was a 51% attack in this post.
Meanwhile and previously Coinbase had reported that it found that there was a 51% attack / reorg attack / double spend attack.
In short, different entities have been looking into what is going on, including some of the main figures behind ETC development and Coinbase. Coinbase thought it found proof of double spending, the ETC devs haven’t come to the same conclusion so far (although everyone agrees something is going on, the details aren’t 100% clear and agreed on).
If some early reports are true, then a group of miners consolidated 51%+ of hash power and used that to rewrite a version of the ETC blockchain where 88,500 ETC was double spent. It is unclear how things will play out, but for now most exchanges have upped confirmation times.
UPDATE: It was later claimed that the attack appeared to be bigger than first reported. Coinbase later detected 12 additional reorganizations that included double spends, totaling 219,500 ETC (~$1.1M).
On 1/5/2019, Coinbase detected a deep chain reorganization of the Ethereum Classic blockchain that included a double spend. In order to protect customer funds, we immediately paused movements of these funds on the ETC blockchain. Subsequent to this event, we detected 12 additional reorganizations that included double spends, totaling 219,500 ETC (~$1.1M).
In all the damage done seems to be limited, and ETC’s price has mostly steadied after dropping a bit when word of the potential attack spread.
Consider, there are 107,350,288 ETC in circulation and the incident was over 219,500, and ETH started the day at $5.45 and is now trading at $5.
Until more is known there isn’t a ton to report, but for more reading see:
TIP: If you want to be extra safe, don’t move your ETC around (between wallets and exchanges) until it is confirmed that everything is OK. On exchanges that are still allowing trading you can still trade freely on exchange. That said, some exchanges have paused trading.