When top aides to US President Donald Trump recently discussed military strikes against Yemen's Houthi militants, they turned to Signal—a messaging app prized for its secrecy. But their plans hit an awkward snag: Jeffrey Mark Goldberg, a journalist and editor-in-chief for The Atlantic, was accidentally added to the encrypted group chat, sparking calls for a congressional probe into whether classified information was mishandled.

So, what is Signal? Launched in 2014, it's a free, open-source app that promises ironclad privacy. Signal uses 'end-to-end encryption', meaning only the sender and recipient can read messages—not even Signal itself. Users' chats, calls, and contacts stay on their devices, not central servers, and conversations can be set to auto-delete. The app stores minimal data: just phone numbers, sign-up dates, and last login times. No ads, no tracking.  

This vault-like security has made Signal a favourite for everyone from privacy activists to politicians—and, as the Trump team's blunder shows, government officials, states a recent report by Reuters. The US Senate approved it for staffers in 2017, and the European Commission advised its use in 2020. Even Elon Musk's team coordinating federal cuts, and protesters opposing those cuts, rely on it. According to the Reuters report, "Let's take this to Signal" is Washington code for "this chat is about to get interesting."

But no system is foolproof. While Signal's encryption is virtually unbreakable, experts warn that if a phone is hacked, all its Signal messages become readable. This hasn't stopped its rise: US downloads jumped 25% year-on-year in early 2025, per analytics firm Sensor Tower. Over 1,100 U.S. state officials and countless congressional aides reportedly use it, according to a recent review by the Associated Press.

Signal's founders—entrepreneur Moxie Marlinspike and president Meredith Whittaker—built it as a nonprofit, vowing never to sell to Big Tech. WhatsApp co-founder Brian Acton, who left over data-privacy clashes with Facebook, bankrolled it with $50 million in 2018. Notably, WhatsApp itself licenses Signal's encryption for its messages, according to Signal's official website.  

Yet the app's secrecy cuts both ways. While journalists and whistleblowers use it to leak safely, drug dealers and January 6 rioters have also exploited it, per law enforcement reports.  For now, the incident has reignited debates about balancing security with accountability. As such, the Trump team's mishap represents a broader tension: Signal is trusted by those guarding power and those fighting it.