Hacker stole 807,260 ETC ($ 5.6 million) in 51% Attack
Ethereum Classic network was attacked and hacker stole ETC worth 807,260 ($ 5.6 million).
According to published information, the attack was to take place between 31 July and 1 August. The attacker was to perform 2 attacks and stole a total of 807,260 ETC worth $ 5.6 million. This attack was to cost the attacker 17.5 BTC ($ 192K) to secure the necessary hash power.
The attacker relied on a strategy of not publishing any blocks but creating private transactions
Bitquery, company dedicated to solve blockchain data problems, published a specific Attack Timeline:
July 29–31. The attacker withdraws 807K ETC from a Crypto exchange to several wallets.
Jul 31, 16:36 UTC. The attacker started mining blocks by purchasing the hash power for double price from Nicehash provider daggerhashimoto, as we found in the first article. The total cost of mining is approx 17.5 BTC ( ~$192,000 )
Jul 31, 17:00–17:40 UTC. The attacker created private transactions, sending money to his/her own wallets, and inserted these transactions in the blocks he/she was mining. No one saw these transactions because the attacker didn’t publish the blocks.
Jul 31, 18:00– Aug 1, 2:50 UTC. The attacker sends money back to the Crypto exchange using intermediary wallets on the non-reorged chain, which was visible to everyone. During this, the attacker has plenty of time to monetize this money — convert to USD and withdraw or change them to BTC, whatever. Long attack duration(12 hours) allowed attackers to split operations into smaller parts to avoid any suspicion.
Aug 1, 4:53 UTC, the attacker publishes his/her blocks with the version of the transaction created in step #3 and executed the chain re-organization. It means that transactions on step #4 replaced with transactions on step #3.
The transfers were apparently made between wallets belonging to the OKEx cryptocurrency exchange, as confirmed by Victor Fang, CEO of Blockchain Ecosystem Intelligence Anchain.ai.
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