This is Signal, the app where government officials shared military secrets with a journalist: how does it work?

Did you hear the one about the United States government officials who accidentally shared military secrets with a journalist via Signal? Sorry, it’s not a joke. If only.

That’s right, the encrypted messaging app known, to some degree, for its privacy features was involved in this gaff by Trump’s senior defense team, raising question about how it could happen. It’s the same app used by activists, whistleblowers, and, it now seems, top U.S. officials coordinating military action. But what exactly is Signal, and how does it work?

What is Signal?

Signal is an end-to-end encrypted messaging app designed for secure communication. It offers texts, voice and video calls, group chats, disappearing messages, and file sharing – all protected by encryption that prevents anyone, including Signal itself, from accessing the content. Sounds good, right?

Developed by the non-profit Signal Foundation, the app is open-source, meaning its code is publicly available for scrutiny. Unlike competitors such as WhatsApp and Telegram, Signal does not collect metadata or store user conversations on its servers, making it one of the most secure communication tools available. Assuming you don’t invite the wrong people to your group!

How do people join Signal chats?

To create or join a group on Signal, users must be invited via their registered phone number. Group administrators control membership and can enable additional security measures, such as disappearing messages. But as recent events have shown, even a highly secure app can’t prevent human error.

Despite its security, Signal can’t stop users from mistakenly adding unauthorized people to group chats – which is exactly how respected journalist Jeffrey Goldberg ended up in a U.S. government group discussing military action against Yemen’s Houthis. National Security Adviser Mike Waltz and his team had used the app to coordinate responses, and Defense Secretary Pete Hegseth reportedly shared classified attack plans just hours before U.S. strikes. Espionage Act, anyone?

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