What is Signal? Everything you need to know about Elon Musk's app recommendation

Tech mogul Elon Musk -- known as widely for slinging cars into the sun's orbit as he is for advocating against COVID-19 safety measures -- took to Twitter earlier this month to slam Facebook over its latest privacy policy updates for its supposedly secure encrypted messaging app WhatsApp. Musk instead recommended people choose encrypted messaging app Signal. 

The tweet was then retweeted by Twitter CEO Jack Dorsey. Shortly after, Signal tweeted that it was working to handle the surge of new users. 

The Signal app was downloaded almost 1.3 million times on Jan. 11, according to data from Apptopia, a tracking firm. The app had been downloaded an average of 50,000 times a day prior to Musk's tweet. A Signal spokesperson said the report undercounted the number of downloads the service is experiencing.

Signal also attributed a temporary outage later that week to the surge in new users. 

"While we have been working hard all week to keep up with all the new people switching over to Signal, today exceeded even our most optimistic projections. We are working hard to resolve [the issue]," the spokesman told CNET in an email. 

Musk's Twitter endorsement also incidentally led shares in the biotechnology company Signal Advance to soar, despite the fact that it is completely unrelated to Signal, which is not a publicly traded company. 

This isn't the first time Musk has publicly sparred with Facebook over privacy concerns. In 2018, he not only had his own personal Facebook page removed, but those of his companies Tesla and SpaceX . His take on the long-fought battle between Signal and WhatsApp isn't off-base, though. 

Both of the encrypted messaging apps have been found to have security bugs over the years that have been resolved. For years, WhatsApp has openly collected certain user data to share with parent company Facebook. Its latest policy change just expands that. Signal, on the other hand, has a history of fighting any entity that asks for your data, and adds features to further anonymize you where possible. 

Read more: Signal vs. WhatsApp vs. Telegram: What to know before you switch messaging apps

Soon after Musk's tweet, WhatsApp published an FAQ aimed at clarifying its data collection policy, emphasizing that neither it nor Facebook can see users' private messages or hear their calls. Following mounting privacy concerns, WhatsApp announced Friday it would delay the rollout of its new policy by three months.

"We're now moving back the date on which people will be asked to review and accept the terms. No one will have their account suspended or deleted on February 8. We're also going to do a lot more to clear up the misinformation around how privacy and security works on WhatsApp. We'll then go to people gradually to review the policy at their own pace before new business options are available on May 15," the company said in a blog post. 

Here are the basics of Signal you should know if you're interested in using the secure messaging app. Plus, here are all of the differences between Signal, WhatsApp and Telegram.

What Signal is, and how encrypted messaging works 

Signal is a typical one-tap install app that can be found in your normal marketplaces like Google's Play Store and Apple's App Store, and works just like the usual text messaging app. It's an open source development provided free of charge by the non-profit Signal Foundation, and has been famously used for years by high-profile privacy icons like Edward Snowden.

Signal's main function is that it can send text, video, audio and picture messages protected by end-to-end encryption , after verifying your phone number and letting you independently verify other Signal users' identity. You can also use it to make voice and video calls, either one-to-one or with a group. For a deeper dive into the potential pitfalls and limitations of encrypted messaging apps, CNET's Laura Hautala's explainer is a life-saver. But for our purposes, the key to Signal is encryption.

Despite the buzz around the term, end-to-end encryption is simple: Unlike normal SMS messaging apps, it garbles up your messages before sending them, and only ungarbles them for the verified recipient. This prevents law enforcement, your mobile carrier and other snooping entities from being able to read the contents of your messages even when they intercept them (which happens more often than you might think). 

When it comes to privacy it's hard to beat Signal's offer. It doesn't store your user data. And beyond its encryption prowess, it gives you extended, onscreen privacy options, including app-specific locks, blank notification pop-ups, face-blurring anti-surveillance tools, and disappearing messages. Occasional bugs have proven that the tech is far from bulletproof, of course, but the overall arc of Signal's reputation and results have kept it at the top of every privacy-savvy person's list of identity protection tools. 

For years, the core privacy challenge for Signal lay not in its technology but in its wider adoption. Sending an encrypted Signal message is great, but if your recipient isn't using Signal, then your privacy may be nil. Think of it like the herd immunity created by vaccines, but for your messaging privacy. 

Now that Musk and Dorsey's endorsements have sent a surge of users to get a privacy booster shot, however, that challenge may be a thing of the past.