DESCRIPTION OF EVENTS
"We have just seen an extremely long attack chain of over 1300 blocks on July 10, 2020, against the BTG network which have been mined since July 1, 2020."
"We detected this illicit activity early on and sent alerts to pools and exchanges to protect them; many closed their wallets over a week ago. We also supplied them with BTG version 0.17.2, which included a checkpoint at block 640650, hash 000000059ec8884fa4fbbdbe46c09cfb4ecba281dfa2351a05084e817c1200ae from July 2 at 2am UTC, mined by MiningPoolHub, a known honest block."
"With this block checkpointed, the attacker’s chain could not take over, but this information was not public, and the attacker continued to mine. The attacker mined their secret chain for nearly 10 days, renting power from NiceHash to do so. Today, on July 10, the attacker released over 1300 blocks."
"Because those attacking blocks are anchored at a block mined on July 1st (before the checkpoint), the honest pools and exchanges who are running the updated code automatically rejected the attacker’s chain."
"July 10, 2020 - Bitcoin Gold 51% attempt. Nodes checkpointed after a tip off."
"[A] strong majority of the honest mining pools have already upgraded their code a week ago, and continue to mine on the honest chain."
This was an unsuccessful 51% attack against Bitcoin Gold. The network was upgraded to reject the hacker's chain due to a tip-off, and avoided any reorganization.
Not only were the attackers not successful. They lost the funds they spent on mining and any other exchange fees related to the attack.