A magazine journalist was unexpectedly included in a group chat of U.S. national security officials on the Signal messaging app, just hours before President Donald Trump authorized airstrikes against Iran-backed Houthi rebels in Yemen. The National Security Council is investigating how the journalist's phone number was added to this secure communication channel. Signal is an application that supports direct messaging, group chats, and voice and video calls, employing end-to-end encryption. It allows for group chats of up to 1,000 participants and includes a feature for messages to self-destruct after a set period. Signal is considered secure but not immune to hacking, and it raises concerns about compliance with open records laws. Government officials are increasingly using encrypted messaging applications, with many having accounts linked to government-issued and personal cell phones. Signal was created by Moxie Marlinspike, who combined two open-source applications, and is overseen by the nonprofit Signal Foundation, which operates without advertisers or investors.