The Ethereum Classic (ETC) blockchain has suffered its third 51% attack this month, as hackers haven ow reorganized over 7,000 blocks on its blockchain, equivalent to two days’ worth of mining.

Mining firm Bitfly, the parent company of the Ethermine mining pool and the first to spot the 51% on ETC earlier this month, was the first to report on the attack, which was later on confirmed by the developers behind the Ethereum Classic blockchain.

The first two attacks on Ethereum Classic reorganized 3,693 and 4,000 blocks respectively, and saw hackers double-spend millions worth of ETC tokens. While the amount lost in the third attack remains unclear, it appears to have been the largest one.

Its timing is notable as it came shortly after one of the main organizations behind Ethereum Classic, ETC Labs, announced a multi-stage plan to thwart future 51% attacks. The plan included defensive mining to stabilize the network’s plummeting hashrate ETC Cooperative, another prominent foundation supporting Ethereum Classic, revealed on social media it was aware of the attacks and “working with others to test and evaluate proposed solutions as quickly as possible.”

Etheruem Classic’ hashrate remains notably low. It shares the same hashing algorithm as Ethereum, but while ETH has a 205 TH/s hashrate, Ethereum Classic only has 2 TH/s. On hashrate renting marketplaces like NiceHash, it’s possible to rent enough hardware to control 51% of ETC’s network, according to Crypto51. In theory, it would cost little over $5,300 an hour to attack the network.

As CryptoGlobe reported, in the first two 51% attacks cryptocurrency exchange OKEx lost $5.6 million to a double-spend attack. In light of the network’s state and its losses, the exchange considered delisting the cryptocurrency. To protect itself, Coinbase extended deposit and withdrawals confirmation times to roughly two weeks.

Featured image via Unsplash.