What Is Signal, The Chat App Used By Us Officials To Share Attack Plans?

A magazine journalist's account of being added to a group chat of U.S. national security officials coordinating plans for airstrikes has raised questions about how highly sensitive information is supposed to be handled.

Atlantic Editor-in-Chief Jeffrey Goldberg detailed a discussion that happened over the Signal messaging app hours before strikes on Iran-backed Houthi-rebels in Yemen ordered by U.S. President Donald Trump.

The National Security Council has since said the text chain "appears to be authentic" and that it is looking into how a journalist's number was added to the chain.

Here's a look at the app in question.

What is Signal?