Double Spending Attack

A double spending attack occurs when a digital currency user successfully spends the same unit of value more than once. In traditional banking, this is prevented by a centralized ledger that tracks every transaction in real-time.

In decentralized systems, this risk is mitigated by consensus mechanisms that order transactions chronologically and prevent conflicting entries from being finalized. An attacker typically attempts this by creating a fork in the blockchain or reversing a confirmed transaction through massive computational power or validator collusion.

Once a transaction is considered finalized, reversing it becomes mathematically and economically prohibitively expensive. The double spending problem is the fundamental issue that blockchain technology was invented to solve.