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I'm trying to get all historical rollbacks of Bitcoin and Ethereum. I get that there were hard-forks (e.g. DAO incident for Ethereum). How about rollbacks because of attack or miners failed to validate the block, etc.? Appreciate it if anyone knows or can point me to some external resources

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Apart from Ethereum uncles and Bitcoin orphans which are tiny forks that happen all the time, these were two instances that I found related to bitcoin bugs:

https://en.bitcoin.it/wiki/Value_overflow_incident: rolled back by community patch https://en.bitcoin.it/wiki/DOS/STONED_incident: no rollback needed

To answer your question, the blockchain can never be rolled back due to failure of miners to validate a block. By definition, a block gets added once a miner validates a block. If all miners suddenly turned off their equipment, no blocks would be produced, and transactions would sit in mempool until some miner took advantage of the extremely low difficulty and started producing blocks again.

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    Thank you. I was thinking that if someone broadcasts a block with fake transactions (with nonce found), and if other miners don't fully validate it and but instead accept it and keep building on top of it, then temporarily this would be the longest chain, right? If in the future, this error is detected and people stop mining this chain, then the blockchain is "rolled back". Did it never happen? or my usage of the term "rollback" is not accurate. – Will Gu Apr 2 '18 at 3:47
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    Also this: bitcoin.org/en/alert/2013-03-11-chain-fork – MCCCS Apr 2 '18 at 6:02
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    Good question. The whole bitcoin network uses a series of checks at each node; the two most important being 1) actual BTC available in the account 2) that the transaction was signed with the appropriate private key. If you ran a bitcoin node that didn't have these checks, you would be in the very deep minority (far less than 51%) and you would be mining false blocks that would never get accepted by the rest of the bitcoin network. – Nicolas Lopez Apr 2 '18 at 12:53
  • It's possible that you could have ~10% of miners on board with your series of transactions, and thereby create a fork that can also be mined (like Bitcoin Cash). However, the rest of the Bitcoin network continues as usual with no "rollback" needed. – Nicolas Lopez Apr 2 '18 at 12:55
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    understood. I'm accepting your answer. Thanks again – Will Gu Apr 3 '18 at 3:44

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