Signal is having a moment. 

Over the past few days, it became the number one free app in the iOS App Store and the Google Play Store, largely because of three things entirely out of its control. The first was the move by both Facebook and Twitter to block President Trump from their platforms, which drove many of his supporters to look for alternatives.

Then, one of those alternatives, Parler, was removed by both Apple and Google from their respective app stores because of information that linked some users of the right-wing friendly social media app to the attack on the U.S. Capitol Building. Parler later went offline entirely when Amazon terminated its AWS account. 

Finally, WhatsApp updated its privacy policy earlier this week, and required users to accept that it shares some information with Facebook before continuing to use the app. The confusion around the change and the mishandling of the rollout caused people to worry it was just another Facebook data grab. In response, Elon Musk tweeted out "Use Signal" to his 42 million followers. 

As a result, people flocked to the encrypted messaging app, which is backed by the nonprofit Signal Foundation. On Monday alone, Signal Messenger was downloaded by more than 1.5 million users. According to Sensor Tower, which provides mobile app analytics, Signal was downloaded 17.8 million times during the week of January 5. That's quite extraordinary for an app that usually averaged around 50,000 downloads per day. 

The surge in downloads even caused issues with Signal's verification system, causing delays in setting up accounts for new users. 

Signal is still the underdog

WhatsApp is still the most popular messaging app, with more than two billion monthly users, despite its recent privacy policy mess. Signal, on the other hand, had around 20 million app installations at the end of last year, according to App Annie, an app analytics platform. 

The reason, however, that the diverse group of users suddenly descended on Signal has much more to do with what happened long before last week. That's important, because even though millions of people may be hearing about it for the first time, it didn't just suddenly appear out of nowhere. 

Signal's previous moment in the spotlight came during Black Lives Matter protests over the summer. At that time, it was a reflection of the app's popularity among activists, journalists, and other security-minded users who value the fact that Signal messages are never stored on the platform's servers and can only be decrypted by the intended end user.

An overnight success, years in the making

Signal was co-founded by Brian Acton, who also founded WhatsApp. After the latter was acquired by Facebook, Acton left and created the nonprofit to develop an open-source encryption protocol, which--ironically--was later adopted by WhatsApp as well.

One major difference, however, is that Signal's privacy protections are good enough that when the company was required to hand over information about a user by a grand jury subpoena, the only information available was the date the account was created, and the date of last activity. There was no information about any of the user's messages or contacts at all.

Even if someone were able to intercept an encrypted message, it would simply look like a jumbled mess. Only the intended recipient, with the correct security key, is able to decrypt it. Signal encrypts all conversations by default. You can't turn it off, even if you wanted to.

That's different from another app that's been having quite a week. Telegram shot up to the number two app on the iOS App Store at the same time as Signal, with more than 400 million users. While Telegram does offer end-to-end encryption, it is off by default, and it can't be used on channels within the platform. 

Privacy is in the spotlight

If nothing else, it's a good thing that people are starting to pay attention to the way many social media platforms treat your personal information. While WhatsApp's new privacy policy isn't actually much different than it was before, the fact that people are so concerned is indicative of how they feel about big tech companies like Facebook, which monetize your personal information as a business model. 

Signal is different, not just because it has fancy cryptography protecting your conversations, but because it was set up from the beginning to be different. The company doesn't show ads. It doesn't sell your information. It doesn't even charge money. As a nonprofit, it exists for a purpose, and is supported by donations.