What Is the Concept of “Long-Range Attacks” Specific to PoS Systems?

Long-range attacks are a class of attacks unique to PoS where an attacker uses old, unspent private keys to create an alternative history (chain) from the very beginning of the blockchain. Since there's no computational cost (hashrate) involved in re-mining old blocks, an attacker who controlled a majority of the stake early on could theoretically rewrite history.

Mitigation often involves checkpoints and relying on social consensus.