Several members of the President Donald Trump administration, including Defense Secretary Pete Hegseth and national security adviser Mike Waltz, are in the spotlight after reportedly sharing plans for bombing Houthi rebels with a reporter in a group chat.

A messaging app called Signal was recently the preferred communications platform for top officials in the Trump administration to discuss war plans.

The chat app, which is run by a nonprofit foundation, has been downloaded 220 million times. Here’s what to know about Signal, including who owns it and whether it’s safe to use.