Overview
A double spend is an attack where the same funds are spent twice by exploiting a chain reorg or fork. It threatens the integrity of digital money. Consensus mechanisms prevent it.
How It Works
An attacker broadcasts conflicting transactions to different parts of the network, then mines a competing chain to make one of them canonical. If the attack succeeds, the other payment is reverted. Proof of work and proof of stake make this costly.
Why It Matters
Double spend prevention is the core security property of blockchains. Its failure would destroy trust in a currency. Confirmations and consensus design mitigate the risk.
Related Concepts
Double spends relate to Transactions, Consensus, and Reorgs. They are prevented by Proof of Work and Finality.