The app has no ads, does not track users' data, and does not store any metadata such as timestamps, internet addresses or group names so it can't give them up if asked. It is considered one of the most secure systems in the world. A company called Whisper Systems created two encrypted apps, RedPhone for voice calls and TextSecure for texting.

The president of Signal defended the messaging app's security on Wednesday after top Trump administration officials mistakenly included a journalist in an encrypted chatroom they used to discuss a looming U.