Miners hash candidate blocks repeatedly until one meets the difficulty target. The work is deliberately wasteful: its cost is exactly what makes rewriting history prohibitively expensive, because an attacker would have to redo it faster than the honest network.
Bitcoin, Litecoin, Dogecoin, Bitcoin Cash and Ethereum Classic all use proof of work. Ethereum did until September 2022.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.
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