() 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.

The Atlantic’s Jeffrey Goldberg said he was aware of the strikes in Yemen, including details on timing and location, before they happened because Waltz added him to a group chat on Signal.

Here’s what you need to know about the messaging app.

What is Signal?

Signal is a free, encrypted messaging app. It can be used for individual and group chats, as well as phone and video calls, so third parties can’t listen in or intercept them.

Signal uses end-to-end encryption, where messages are scrambled during transmission, and only the sender and receiver have the key to decrypt them.

The encryption protocol used by Signal is open source, which makes it free for anyone to use. The same protocol is used in other messaging services, including WhatsApp.

The app can also be set to delete older messages after a period of time.

Who uses Signal?

Signal is used by government officials, but it is not meant to be used to discuss classified information, and it is not supposed to be downloaded on government-issued devices.

Signal is also popular with journalists, protesters, activists and dissidents. CEOs, whistleblowers and average people who want a more secure way to text also use Signal.

The app has also been used by criminals, including those involved in organized crime.

Is Signal secure?

Signal is considered one of the most secure, publicly available messaging apps. But that doesn’t mean it’s impossible for the app to be hacked, and researchers recently found Russian military hackers were targeting Signal.

One security risk is that Signal can be linked to devices, including desktop or laptop computers, where information could be accessed by malware on those devices.

While government officials have previously used Signal for organizational messages, it does not have the level of security needed for discussing classified information.

Who owns Signal?

The app was originally developed by an entrepreneur who was briefly head of product security at Twitter (now X). He goes by the name Moxie Marlinspike and built the app based on two other open-source apps.

It is now run by the nonprofit Signal Foundation, which was set up in 2018. According to the foundation’s website, it has no investors or advertisers.

Could using Signal violate federal records laws?

Government communications, especially those at the highest levels, are subject to laws regarding security and preservation, namely the Presidential Records Act and the Federal Records Act. Using Signal for certain types of communication could be a violation.

The Presidential Records Act mandates the use of government-approved communications channels for all work-related conversations. Using Signal would potentially violate the law, especially if classified information were mishandled.

The Federal Records Act requires government communications to be preserved by the National Archives so they can eventually be declassified and may be accessed for Freedom of Information Act requests. If an app like Signal is used, government employees are supposed to copy messages to a government device for preservation.

Signal’s disappearing message function would be a violation of the law if those messages were not transferred and preserved elsewhere.