What Is the Economic Cost of Performing a One-Hour 51% Attack on a Major Altcoin?

The economic cost of a one-hour 51% attack is a function of the coin's total hash rate and the current market rate for renting that much hash power. For major altcoins, this cost is often estimated by services that track hash rental markets.

While significantly lower than Bitcoin's, the cost is still substantial and is the primary defense for smaller PoW chains. The attack's success also depends on the depth of the chain to be reorganized and the potential profit from the double-spend.