intermediate
an attack on a blockchain by a group of miners who control more than 50% of the network's mining hash rate

51% Attack

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A 51% attack represents the situation where more than half of the computing power “Hashrate” refers to the total combined computational power that is being used to mine and process transactions on a Proof-of-Work blockchain. “Hashrate” refers to the total combined computational power that is being used to mine and process transactions on a Proof-of-Work blockchain, such as Bitcoin and Ethereum.Learn more within a given blockchain is of one person or one concentrated group. This ensures that this group gains full control over this blockchain.

The attackers would be able to prevent new transactions from gaining confirmations, allowing them to halt payments between some or all users. They would also be able to reverse transactions that were completed while they were in control of the network, meaning they could double-spend Double-spending is the risk that a digital currency can be spent twice. Double-spending is the risk that a digital currency can be spent twice.Learn more coins.

They would almost certainly not be able to create new coins or alter old blocks. A 51% attack would probably not destroy BitcoinBitcoin1$ 64,051.810.18%-6.01%-15.89%details or another blockchain-based currency outright, even if it proved highly damaging.

Those who cannot attack the thought, instead attack the thinker.

Paul Valéry
French poet