How Does a Sudden Drop in Hash Rate Affect a PoW Chain’s Security?

A sudden, significant drop in a Proof-of-Work (PoW) chain's hash rate makes the network more vulnerable to a 51 percent attack. Since the difficulty adjustment is not instantaneous, an attacker needs less computational power to control a majority of the remaining hash rate.

This temporary vulnerability increases the risk of double-spending and chain reorganization until the difficulty adjusts downward to reflect the new, lower hash rate.