Definition ∞ A chain history rewrite describes an alteration to a blockchain’s historical record, effectively changing past transactions or block order. This event typically occurs due to a 51% attack or a hard fork, where a new, longer chain supplants the previous one. Such a rewrite compromises the immutability principle fundamental to blockchain technology. It can lead to double-spending and a loss of trust in the network’s integrity.
Context ∞ The possibility of a chain history rewrite remains a significant security concern for proof-of-work blockchains, especially those with lower hash rates, making them vulnerable to concentrated mining power. Recent news often reports on potential threats or successful minor reorganizations, which highlight the importance of sufficient network decentralization and computational security. The debate continues regarding the necessary safeguards and economic incentives to prevent such disruptive events.
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