A 51% attack is when the hacker can control a majority of mining power on the Proof-of-Work blockchain network, i.e. the majority block verifier could prevent other users from mining and reverse transactions. Though many may assume that such an attack is with malicious intent, this scenario seems to be different.
As per Swann the two miners with majority control of the network are BTC.top and BTC.com. The duo’s attack was to stop that unknown miner from taking coins that were sent to an “anyone can spend” address following the original hard fork in May 2017. As per Swann’s tweets:
The Tweets
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Since the original split in 2017, there has been a significant number of coins accidentally sent to “anyone can spend” addresses (due to tx compatibility of sigs, but no #SegWit on #BCH), or possibly they’ve been replayed from #Bitcoin onto the #BCH network.— Guy Swann ?[Pay me in Bitcoin] (@TheCryptoconomy) May 24, 2019
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In the confusion, an unknown miner (possibly the attacker, but unconfirmed) tried to snatch a bunch of P2SH/#Segwit coins. But https://t.co/gZNf6P1G3l & https://t.co/h08wTM6XgZ were expecting, and/or preparing to recover SegWit coins themselves…https://t.co/jNzqgOh4km— Guy Swann ?[Pay me in Bitcoin] (@TheCryptoconomy) May 24, 2019
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So just 2 miners, in secret & w/ no trouble, took it upon themselves to remove 2 blocks w/ another’s TXs, & replace with their own.Bizarrely, some are celebrating!
Some devs are quiet, but jtoomim (#BCH dev) called it “justice,” & “punishment” for “antisocial behavior.” pic.twitter.com/ntiaV21YBG
— Guy Swann ?[Pay me in Bitcoin] (@TheCryptoconomy) May 24, 2019
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Very curious to see others who could dig further (& more thoroughly) into this, as details are not easy to find, & there seem to no articles about the 51% as far as I can tell. ?/fin@nic__carter @DZack23 @MessariCrypto @BitMEXResearch @jimmysong @AaronvanW @TuurDemeester
— Guy Swann ?[Pay me in Bitcoin] (@TheCryptoconomy) May 24, 2019