Earlier on 1st August, several figures related to Ethereum Classic [ETC] took to Twitter to tell the community of issues with the ETC blockchain. Among the primary was Ethereum Foundation member Hudson Jameson who added that: “Exchanges need to pause deposits and withdrawals.”
The official Twitter page of ETC and James Wo, founder of Ethereum Classic Labs, both confirmed the issue. A Diagnosis report was soon released to explain what happened. Although the offending miner was identified, it had been not clear if it was a deliberate attack on the network.
The report revealed that miners should “Continue mining the chain as-is,” adding that any transactions issued during the earlier 12-hour period were possibly not mined within the same order they were alleged to be, but they will be re-submitted back to the mempool.
As suggested by a mining solutions provider Bitfly, a network reorganisation of 3693 blocks has taken place at block 10904146. Consistent with the message: “This caused all state pruned nodes to prevent syncing,” suggesting a 51% attack on the network.
Reorg is an inbuilt feature within a blockchain that permits to roll back the network. However, if malicious miners secure 51% of the hashpower, they can split the network, double spend or erase previous transactions.
At the starting of 2019, a confirmed 51% attack on ETC took place, raising concerns around the Proof-of-Work mining model.