What to know about Signal, which the Pentagon previously discouraged workers from using

As the White House comes under fire for allegedly using Signal to discuss sensitive foreign policy plans, the encrypted messaging platform has now come into the spotlight.

Although the government has officially discouraged federal employees from using the app for official business, it has become a crucial tool for many businesses, tech enthusiasts and the public for sharing messages securely.

Signal was launched in 2014 for iOS devices by a non-profit group, Open Whisper Systems, which offered users free encrypted calls and, one year later, encrypted instant messaging. Encryption disguises data and information so that only those who send and receive the messages can read them.

An Android version of the app launched in 2015. Both versions are free to download in the app stores.

"Signal is designed to never collect or store any sensitive information. Signal messages and calls cannot be accessed by us or other third parties because they are always end-to-end encrypted, private, and secure," the company said on its website.

Representatives from Signal Technology Foundation, the parent non-profit that operates the app, didn't immediately respond to ABC News' request for comment.

The app registers users through their phone numbers, similar to WhatsApp and iMessage, and provides several options, including disappearing messaging and protection from screenshotting messages. Signal has touted that it does not give user data to corporations and other entities.

Signal group chats, like the one at the center of the Trump administration scandal, are controlled by users designated as administrators. The administrators have the power to invite, reject and block users at will.

Encryption keys for Signal messages are stored on the user's devices and not on its servers, the company said.

Stuart Madnick, a professor at MIT's Sloan School of Management and the founding director of Cybersecurity at MIT Sloan, told ABC News that while end-to-end encryption on apps like Signal are secure, there are still ways that messages can be compromised through analog and digital tactics.

If a device is physically stolen along with unlock codes, there is nothing stopping an alleged thief from opening the Signal app and reading messages, he said. Additionally, malware and other spying software can gain access to messages, according to Mardnick.

"It's the on and off ramps that keep us susceptible," he said.

Atlantic editor-in-chief Jeffrey Goldberg said in his piece and told ABC News that he was invited to the Signal chat by someone claiming to be National Security Adviser Mike Waltz and at first thought it was a hoax until he relaized it was a legitmate group chat with chief Trump officials.

"I watched this Yemen operation go from beginning to apparent end, and that was enough for me to learn that there's something wrong in the system here that would allow this information to come so dangerously close to the open, to the wild," Goldberg told ABC News.

Madnick said the situation described by Goldberg also showed another vulnerability by using public end-to-end encryption messaging: slip-ups by a user who sent messages to the wrong person.

Signal grew in popularity among smartphone users and have been promoted by various figures in the tech community, including Edward Snowden.

Despite its growth, U.S. government officials have been wary of members using the app for official business.

The Pentagon's internal watchdog criticized a former official's use of the Signal app in 2021, calling it a breach of the department's "records retention policies" and an unauthorized means of communicating sensitive information.

The report, which focused on Brett Goldstein, a former director of the Defense Digital Service, found that Goldstein violated department policies by using Signal "to discuss official DoD information" and encouraging subordinates to communicate with him on the encrypted messaging app.

"Signal is not approved by the DoD as an authorized electronic messaging and voice-calling application," the report asserted, adding that "the use of Signal to discuss official DoD information does not comply with Freedom of Information Act requirements and DoD's records retention policies."

Goldstein had already announced his plans to depart government service by the time the report was published. According to the report, Goldstein lobbied the department's legal office to allow him to use the app.

"We recommend that the Secretary of Defense take appropriate action regarding Mr. Goldstein's use of the unauthorized electronic messaging and voice-calling application," the report concluded.

During a Senate Intelligence Committee hearing on Tuesday, Democratic Sen. Mark Warner grilled CIA Director John Ratcliffe about his participation in the Signal chat. Ratcliffe said he was in the chat, but claimed many in the agency are approved to use Signal.

"One of the first things that happened when I was confirmed as CIA director was Signal was loaded onto my computer at the CIA as it is for most CIA officers. One of the things that I was briefed on very early senator, was by the CIA records management folks about the use of Signal as a permissible work use. That is a practice that preceded the current administration to the Biden administration," Ratcliffe testified under oath.

Ratcliffe, and the other intelligence officials who testified, did not provide more details about the government's use of the app or approvals to use it.

Madnick said typically, the government has its own secure communications for sending information but that usually involves specialized devices that are installed in government offices.

"There are a lot of things that the government does to make their conversations more secure but that comes at an inconvenience," he said.

As of 2024, the app has 70 million users worldwide compared to the 12 million who used it in 2020, according to the app tracking site Business of Apps.

In 2023, the non-profit, which is funded through donations and a $50 million investment in 2017 from WhatsApp co-founder Brian Acton, said in a blog post it required $50 million a year to operate in 2025.

"Our goal is to move as close as possible to becoming fully supported by small donors, relying on a large number of modest contributions from people who care about Signal. We believe this is the safest form of funding in terms of sustainability: ensuring that we remain accountable to the people who use Signal, avoiding any single point of funding failure, and rejecting the widespread practice of monetizing surveillance," the company said.

ABC News' Luke Barr, Cherise Halsall and Nathan Luna contributed to this report