Bitcoin Gold's developer team has prevented an "extremely long attack chain" against the network according to a Friday announcement.
According to the development team, an attacker rented hash power from mining service provider NiceHash on July 1 and secretly mined an alternative chain — essentially creating a new transaction history for the network — for nearly ten days, mining over 1,300 blocks in the process. On July 10, the attacker released the secret chain in an attempt to collect over 8,000 bitcoin gold, worth more than $75K at press time.
The attacker was thwarted, however, as the Bitcoin Gold team detected the attack early on and alerted mining pools and exchanges about the potential attack. The team also privately supplied these entities with a new updated version of the Bitcoin Gold network, which implemented a checkpoint at block 640,650—the most recent "honest block" before the attack. This new code, run by pools and exchanges, automatically rejected the attacker's chain when it was released on July 10.
Bitcoin Gold has a history of reorg attacks. The network faced a $70,000 attack in January 2020 and an $18M attack in May 2018.