51% attack

In proof of work, sustained majority hash power can produce a competing branch with more accumulated work. This can exclude operations or reverse the attacker’s own payments to attempt double spending.

The attacker remains subject to validity rules checked by nodes. Hash-power control alone cannot forge other users’ signatures or spend their coins. Cost and feasibility depend on the network and attack duration.

Proof-of-stake systems have specific thresholds for blocking finality or producing conflicts. Automatically applying 51 to every consensus model hides relevant differences.