Definition
A 51% attack (or majority attack) occurs when a single entity or coordinated group controls more than half of the Bitcoin network’s total hashrate. With majority hashrate, the attacker could mine a private chain faster than the honest network and eventually release it to overwrite recent transaction history.
This would allow double-spending (spending the same Bitcoin twice) or transaction censorship. However, the enormous cost of acquiring 51% of Bitcoin’s hashrate (hundreds of billions in hardware and electricity) makes this attack economically impractical. This is why Bitcoin’s high and well-distributed hashrate is essential for security.
In Simple Terms
A theoretical attack requiring over 50% of network hashrate to double-spend or censor transactions.
51% Attack is a term used in Bitcoin mining related to network & protocol.
Also known as: Majority attack, 51 percent attack.
A 51% attack (or majority attack) occurs when a single entity or coordinated group controls more than half of the Bitcoin network’s total hashrate. With majority hashrate, the attacker could mine a private chain faster than the honest network and eventually release it to overwrite recent transaction history.
This would allow double-spending (spending the same Bitcoin twice) or transaction censorship. However, the enormous cost of acquiring 51% of Bitcoin’s hashrate (hundreds of billions in hardware and electricity) makes this attack economically impractical. This is why Bitcoin’s high and well-distributed hashrate is essential for security.
Understanding 51% attack is important for Bitcoin miners because it directly impacts mining operations, hardware selection, or profitability calculations. Whether you are a home miner running a Bitaxe or operating a larger ASIC setup, this concept helps inform better mining decisions.
Related terms: Network Hashrate, Proof of Work, Longest Chain Rule.