51% Attack
Security● Common
An attack where an entity controlling majority hashrate can reverse recent transactions by mining an alternative chain and orphaning honest blocks. Can enable double-spending. Extremely expensive against Bitcoin due to massive hashrate.
Technical Notes
Cost: ~$1M+ per hour to rent majority hashrate (2024). Can only reverse own transactions (can't steal others' coins). Depth of reversal limited by cost. Smaller coins more vulnerable. Countermeasures: more confirmations, monitoring for private mining.
Metadata
Visibility: Public
Created:1/3/2026by System