MW Why would someone use Signal? What to know about the messaging app that Pete Hegseth and other Trump officials have relied on.

By Charles Passy

The chat app, which is run by a nonprofit foundation, has been downloaded 220 million times. Here's what to know about Signal, including who owns it and whether it's safe to use.

The messaging app Signal is making headlines again, with the news that U.S. Defense Secretary Pete Hegseth used it for a chat with his wife, his personal lawyer and others in which he shared sensitive military information.

In late March, Hegseth and other officials in President Donald Trump's administration came under fire when it was learned that they had relied on the encrypted group-chat app to discuss plans for airstrikes against Houthi militants in Yemen - and that they had inadvertently included Atlantic magazine editor Jeffrey Goldberg in their exchange.

All that likely leaves many non-Signal users curious about the app - and how it ended up as the platform for such highly sensitive conversations. Here's what you need to know.

What is Signal?

Signal is an open-source - meaning freely available - service that enables end-to-end-encrypted conversations over voice, text or video via a smartphone or a desktop computer linked to a smartphone. Signal works with devices that utilize Android or iOS operating systems. In terms of its encryption, Signal says on its website that conversations "can only be read or heard by your intended recipients. Privacy isn't an optional mode - it's just the way that Signal works." (Signal didn't respond to a request from MarketWatch for comment.)

As the Wall Street Journal explained about the technology that Signal uses: "Encryption turns your messages and calls into a string of gibberish. Only the intended recipient is able to decrypt the message - no one else, not even the app's maker."

Who uses Signal?

Millions of people - including journalists, political activists and, yes, government officials - use Signal. It's designed for those who want to ensure their conversations are private. Even Tesla $(TSLA)$ CEO Elon Musk once indicated he was a fan of the app, although his message caused some market confusion, because investors thought he was expressing support for Signal Advance (SIGL), a different technology company.

Signal - the encrypted messaging app, that is - had 70 million users in 2024, according to the Business of Apps website. It has been downloaded 220 million times, but the Business of Apps site says most of those downloads occurred in 2021.

Who owns Signal?

Signal is not a public company. In fact, it's not even a for-profit company. It's run by a nonprofit foundation, Signal Technology Foundation, which encourages users to contribute funds. "Donating to Signal helps pay for the servers, bandwidth, and ongoing development to ensure that Signal remains available to the millions of people around the world who count on it to protect their privacy," the Signal website says.

Those donations do add up: Signal reported $35.8 million in revenue in 2023, according to a publicly available tax filing that's required of nonprofit organizations. The filing indicated that the bulk of that money -$22.7 million - came from contributions and grants.

When did Signal launch and who created it?

Signal's roots go back to 2012, according to a separate Signal Foundation website. Two technological innovators - Moxie Marlinspike (aka Matthew Rosenfeld) and WhatsApp $(META)$ co-founder Brian Acton - have been key players behind it. Marlinspike, once described as a "cypherpunk programmer," is credited as the founder on the Signal Foundation site, while Acton is listed as a board member. Acton also put $50 million into Signal's foundation in 2018 to help ensure its future.

Acton said at the time: "As more and more of our lives happen online, data protection and privacy are critical. This isn't just important for select people in select countries. It's important for people from all walks of life in every part of the world."

Is Signal safe to use?

Signal generally gets high marks for doing what it's supposed to do in terms of maintaining users' privacy. PCMag rated it the best overall private-messaging app in a recent survey. "We consider Signal to be an excellent choice for private messaging, and it's easy to see why. All messages are secured with end-to-end encryption (E2EE) and Signal is a nonprofit, so there's no reason to harvest any user data. The underlying technology of Signal is so successful it has been implemented by Google $(GOOGL)$ and Meta (META)," PCMag said in its assessment.

What are the potential disadvantages of using Signal?

An oft-cited issue with Signal is the fact that, as a phone-based system, it comes with the potential risk of someone gaining access to a user's phone - say, if it's stolen or lost. And as the BBC pointed out, "no app can prevent someone peeking over your shoulder if you are using your phone in a public space."

Signal does point to certain safeguards: "If you lose your phone, follow the steps on our support site to re-register for our services. When you register with a new device, your old device will stop receiving all messages and calls," the company says on its website.

Are there alternatives to Signal?

There are plenty of alternatives: PCMag pointed to several private-messaging apps in its survey. Among them are the aforementioned and highly popular WhatsApp, which is owned by Facebook parent Meta. Others include Telegram, Session and Briar. The publication noted strengths and weaknesses for each. For example, it said that Telegram was best for social networking, while Session was best for anonymous texting.

Should government officials use Signal?

A March story in Politico discussed this question at length, noting that while Signal "is viewed as fairly strong due to its robust privacy features," experts agree that "it shouldn't be used by government officials as an alternative to communicating through more secure, sanctioned government communications - which Signal is not."

Pentagon spokesman Sean Parnell said in post on X Sunday night: "There was no classified information in any Signal chat, no matter how many ways they try to write the story. What is true is that the Office of the Secretary of Defense is continuing to become stronger and more efficient in executing President Trump's agenda."

-Charles Passy

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April 21, 2025 10:50 ET (14:50 GMT)

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