What Is the Effect of a Sudden Drop in Difficulty on a Blockchain’s Security?

A sudden drop in mining difficulty, usually following a mass exodus of miners, can temporarily reduce a blockchain's security. While the difficulty is lower, it becomes significantly cheaper and easier for an attacker to acquire 51% of the remaining hash rate.

This vulnerability window persists until the difficulty can readjust upward in the next cycle, assuming new miners are attracted by the increased profitability. The sudden drop itself signals reduced hash rate and higher attack risk.