Bitcoin Cash miners perform 51% attack to undo malicious transactions

Two bitcoin cash mining pools BTC.com and BTC.top combined their hash rates to perform a 51 percent attack on the blockchain to reverse a malicious miner’s transactions. While their intentions were not “evil,” their actions have been criticized widely in the community. As one bitcoin cash developer, going by “Kiarahpromises,” wrote:

“To coordinate a reorg to revert unknown’s transactions. This is a 51% attack. The absolutely worst attack possible. It’s there in the whitepaper. What about (miner and developer) decentralized and uncensorable cash? Only when convenient?”

Some, like BCH supporter Jonathan Silverblood, have supported the actions. As Silverblood puts it:

“This is a very unfortunate situation, but it is also what proof of work actually is. The miners in this case did choose to drop prohashes block and from what I heard, it is because they deemed a transaction within it to have been invalid.”

The attack

Bitcoin podcast host, Guy Swann, explained the inner workings of the original attack that prompted this action. He Tweeted:

“Since the original split in 2017, there has been a significant number of coins accidentally sent to ‘anyone can spend’ addresses (due to [transaction] compatibility of sigs, but no #SegWit on #BCH), or possibly they’ve been replayed from #Bitcoin onto the #BCH network.

When the unknown miner tried to take the coins themselves, [BTC.top and BTC.com] saw & immediately decided to re-organize and remove these [transactions], in favor of their own [transactions], spending the same P2SH coins, [and] many others.”