On July 10, the Bitcoin Gold team saw an extremely long attack chain of over 1300 blocks, which have been mined since July 1, 2020, against the BTG network.
As per the announcement, the team has prevented the attack after detecting it early on and alerting the exchanges and mining pools about the potential attack.
The team released a new updated version of the Bitcoin Gold network at block 640,650, the most “honest” block mined by MiningPoolHub before the attack. This update, which wasn't public knowledge, rejected the attacker's chain when it was released on Friday.
For the attack, the perpetrator rented hash power on July 1 from NiceHash, a mining service provider, to secretly mine an alternative chain. The chain was mined for ten days and was 1,300 blocks long. On July 10, the secret chain was released by the attacker in an attempt to steal 8,000 BTG worth over $75k.
Now, everyone is required to upgrade their nodes to make sure they are on the honest chain.
“51% attack on BTG defeated by a user-activated soft fork providing a checkpoint and hence explicitly banning the attack chain. Excellent news,” commented Ethereum co-founder Vitalik Buterin. “In PoS, in such cases, the attacker would lose many millions of dollars to slashings/inactivity leak,” he added.
Bitcoin Gold might have successfully stopped a block reorganization attack, but it's not the first time such a thing happened. The network has a history of reorg attacks, it faced a $70k attack earlier this year and then back in May 2018 lost $18.6 million in a double spent attack.