Signal, a widely used encrypted messaging app, is facing scrutiny after reports emerged that US national security officials used it to coordinate military operations. The incident came to light when The Atlantic editor-in-chief, Jeffrey Goldberg, revealed he was inadvertently added to a Signal group chat discussing planned airstrikes on Iran-backed Houthi rebels in Yemen.

The National Security Council has since confirmed the authenticity of the messages and is investigating how a journalist’s number ended up in the sensitive conversation. The episode has raised concerns over the use of encrypted messaging apps by government officials and the potential security risks involved.

What is Signal?

Signal is a messaging app that supports text, voice, and video communication. It is widely recognised for its end-to-end encryption, which ensures that only the sender and recipient can access the content of messages or calls. Unlike some other messaging services, encryption on Signal is enabled by default, meaning even the app’s developers cannot access conversations.

Developed as an open-source project, Signal’s encryption protocol is also used by WhatsApp, though WhatsApp is owned by Meta and includes data-sharing policies that Signal does not. Signal offers features such as disappearing messages, group chats with up to 1,000 participants, and phone and video calls—all protected by encryption.

How secure is Signal?

Cybersecurity experts generally regard Signal as one of the most secure messaging platforms available. Signal’s encryption technology prevents interception by third parties, including governments and hackers.

However, while the app itself is secure, user errors—such as mistakenly adding an unauthorised person to a sensitive chat—can still pose risks. Additionally, encrypted messages do not automatically archive on government servers, potentially allowing officials to bypass open records laws.

Meredith Whittaker, president of Signal, defended the app on social media, calling it the "gold standard in private communications" but did not directly comment on the Atlantic report.

Why do government officials use Signal?

Encrypted messaging apps like Signal are increasingly popular among government officials worldwide. According to an Associated Press review, officials in nearly every US state have accounts on such platforms, often linked to government-issued phone numbers.

Under President Joe Biden’s administration, White House officials with permission to download Signal were instructed to use it sparingly. A former national security official revealed that Signal was primarily used to alert someone to check for a classified message through other secure channels rather than to share sensitive information directly.

Despite these precautions, the mistaken inclusion of a journalist in a classified discussion raises questions about how encrypted apps should be used for national security communication.

Who owns Signal?

Signal was created by entrepreneur Moxie Marlinspike, who initially merged two open-source security apps into one encrypted platform. In 2018, WhatsApp co-founder Brian Acton donated $50 million to establish the nonprofit Signal Foundation, which funds the app without relying on advertisers or investors.

What happens next?

The Atlantic report has intensified debates over how government agencies handle classified discussions and whether encrypted apps should be used for such purposes. While Signal remains a trusted platform for privacy-conscious users, the incident underscores the importance of operational security, even on encrypted platforms.