Two bitcoin cash (BCH) mining pools recently carried out what is known as a 51 percent attack on the blockchain in an apparent effort to reverse another miner’s transactions.
The move is tied to the bitcoin cash network hard fork that occurred on May 15. The two mining pools — BTC.com and BTC.top — carried out the move in order to stop the unknown miner from taking coins that they weren’t supposed to have access to in the wake of the code change. That day, an attacker took advantage of a bug unrelated to the upgrade (and subsequently patched) that caused the network to split and for miners to mine empty blocks for a brief time.
In the context of cryptocurrencies like bitcoin cash, a 51 percent attack involves an entity or group controlling a majority of the hash rate which thereby allows them to execute several things they aren’t normally allowed to do, such as attempting to rewrite the network’s transaction history.
At one point BTC.top did alone control more than 50% of the power. But BTC.com and BTC.top they were able to join together to reverse the blocks of transactions. According to stats site Coin.Dance, the two mining pools currently have combined 44% of bitcoin cash hashing power.
The interesting part of this particular attack on bitcoin cash, though, is that it was arguably executed in an attempt to do something ostensibly good for the community, not to reward the attackers or to take the funds for themselves.