Terrorist groups are increasingly using encryption to plan and coordinate terrorist acts, leading to calls for the banning or backdooring of encrypted messaging apps. This would be misguided. It would not remove the ability of terrorist groups to access this technology and may push them to communicate in ways that are more difficult for Western intelligence agencies to monitor. By creating vulnerabilities in online tools used by a very large number of Americans and other users around the world, it would also expose the broader society to increased security risks.