Double spend is a malicious act in the context of blockchain where a user attempts to spend the same digital currency (e.g., Bitcoin) more than once by creating multiple conflicting transactions. Since digital currencies rely on decentralized consensus mechanisms like proof of work, there is a time delay between transaction propagation and confirmation. This delay creates a window of opportunity for an attacker to submit multiple conflicting transactions to different nodes. By controlling a majority of the network's mining power, the attacker can attempt to confirm one transaction and invalidate the other, effectively spending the same currency twice. Preventing double spends is a critical challenge in blockchain systems.
