Two BitCash miners BTC.com and BTC.top executed a 51% attack on the BitCash network to thwart an unknown miner’s transactions.
A 51% attack happens when an individual holds a majority of the hash rate. This situation arose because a bug had split the BitCash network causing the hash rate to drop and allowing miners to mine empty blocks for a brief time.
The unknown miner would have had to hold a lot of BitCash to secure hash rate. He took advantage after realizing he held the majority of the hash rate, which empowered him to manipulate the network. It is speculated that he first sold a lot of BitCash and then submitted a blockchain, which was longer than the one on which the previous transaction was embedded, albeit consisting of empty blocks. It would invalidate the previous blockchain and return the miners BitCash back to him.
BTC.com and BTC.top came together to reverse the unknown miner’s blocks of transactions. Thus, his transaction remained on the blockchain, and the BitCash was not returned to him. In this way, the counter-attack by BTC.com and BTC.top thwarted the unknown miner.
In the wake of the attack, BitCash has stated that it has asked its exchanges to increase the number of confirmations before any BitCoin deposit is recorded on the blockchain. It will increase the length of the blockchain required to replace the original one.
The attack has raised concerns over proof-of-work as a consensus mechanism as well as holding patterns of miners in various cryptocurrencies. In a situation with very few miners, it becomes easy for someone to get majority control of hash rate.
BitCash has clarified that it will not be shifting to a new algorithm but is in talks for making major changes to make such attacks obsolete.