If there was a hard fork in October 2018, it was probably to remove the attacker's blocks.
I am not involved with anything here, actually I didn't even read the thread before posting. I was just checking out NYC on coinmarketcap, and I checked the rich list on the block explorer. There I noticed 32 blocks that said "Mr.51%", and I was like wtf? Inside these weird blocks is a single transaction with the input as the destination address. The balance appears negative.
Not many people understand what a 51% attack means, it is talked about a lot in the original bitcoin white paper.
Because the block times are fast, 300 confirmations are necessary to prevent another 51% attack.
diorthotis, just so you know, the Mr. 51% notations were made by the Community Devs to alert the public of the addresses that were used in the 51% attack. It's helpful to identify the attacker in case any of those addresses are used in subsequent transactions.
You can learn more about the 51% attack from the Medium article posted
https://medium.com/@newyorkcoin/timeline-analysis-and-response-to-recent-51-attack-941da50d625c https://medium.com/@newyorkcoin/timeline-analysis-and-response-to-recent-51-attack-941da50d625c