“If you bribe 51 percent of the miners, they will change the ledger for you. [This] tells you just how little irreversibility there is in PoW coins,” tweeted Cornell University professor and researcher in blockchain consensus protocols Emin Gün Sirer.A 51% attack on the blockchain network is not a new attack vector for PoW blockchains. However, as highlighted by Gün Sirer, it’s also not really an attack vector. On very special instances, the majority of self-interested miners on PoW blockchains have voluntarily agreed to alter a transaction history to undo critical situations.While the situation isn’t entirely the same, in the past, blockchain networks have seen their histories altered in the wake of critical moments. This happened on the ethereum blockchain back in 2016 when over $60 million worth of coins were siphoned off from the now-defunct smart contract The DAO. It also happened on the vericoin blockchain back in 2014 after $8 million worth of coins were hacked.While controversial, both decisions were supported by the primary developer community who launched system-wide upgrades or hard forks to enable otherwise infeasible amendments to the blockchain transaction history.Yet those choices weren’t without their repercussions; the resulting ethereum fork resulted in two distinct chains, ethereum and ethereum classic, respectively.A resounding noStill, many in the bitcoin community took to social media to deride the idea as both infeasible as well against the philosophical underpinnings of the technology.In Binance’s particular case, prominent members of the bitcoin community point out that bitcoin being the world’s largest blockchain is a particularly unique case with a reputation to uphold.“Talk of forking or reorganizing the blockchain is close to heresy,” tweeted billionaire bitcoin investor Michael Novogratz. “When the ethereum community did it the project was like 5 months old. A baby. Bitcoin now has $100bn market cap and is a legitimate store of wealth.”It would also be unfair according to Adam Back – CEO of bitcoin development startup Blockstream – given that the latest Binance hack is nowhere near as severe as previous hacks suffered on the bitcoin blockchain.“A Bitcoin reorg is just not happening, and I doubt any Bitcoin industry, miners nor developers considered it either. Recall 2014 $473mil, 2016 bitfinex hack $72mil, 2019 binance $40mil etc. #NotHappening,” tweeted Back.

Source: What a Bitcoin ‘Reorg’ Is and What Binance Has to Do With It – CoinDesk