The social networking giant did not disclose how much it is paying to acquire the app, but the deal shows that Facebook is ready to jump on an anonymous messaging trend that’s already been around for the past couple of years, as evidenced by a string of flash-in-the-pan apps like Yik Yak, Secret, and After School. Much like its predecessors, tbh seemingly came out of nowhere to gain rapid popularity, reaching the top of Apple’s app store rankings for free downloads in recent weeks despite only launching in August.

According to the app’s description in the Apple app store, 5 million people have already downloaded tbh in just the past few months, and the app reportedly has 2.5 million daily active users.

So far, tbh’s rise has somewhat mirrored that of Sarahah, another anonymous messaging app that was all the rage with teens over the summer. Both Sarahah and tbh are social apps that allow users to send anonymous messages. (Though Sarahah was actually developed as a tool for employees to give honest, anonymous feedback to their employers.)

For Facebook, tbh offers another way to attract more young users, especially as the social network’s own demographic for its namesake service continues to skew older. In the past, Facebook has acquired services like Instagram to cater more to younger users, while the company also regularly copies the features of rival social apps that are popular with young users, especially Snapchat.

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What is the TBH app?

First of all, what does tbh mean? The app’s name comes from the internet shorthand for the phrase “to be honest,” which is fitting considering that the app from parent company Midnight Labs is intended to be a place where users can offer anonymous feedback to people they know online.

Unlike other anonymous messaging apps, though, tbh doesn’t actually allow users to communicate with each other directly. Instead of sending anonymous messages to other users, people on tbh participate in online polls where they anonymously rate their friends in complimentary categories like “Who has the best smile?” or “Makes you laugh the hardest.” The process is completely anonymous, but users receive notifications (and virtual “gems”) when they are selected in a poll, and the sender of a particular poll can also reveal their true identity if they so choose.

The app is currently only available in 34 U.S. states, which makes its rising popularity that much more impressive. And, tbh is clearly aimed at the teenaged demographic, as the app (which is recommended for users aged 12 and up) asks new users when they sign up to either identify what grade they are in, from high school to college, or to select the option “not in high school.”

Is TBH safe?

The app bills itself as “the only anonymous app with positive vibes,” which is an important distinction considering the typical criticism heaped upon previous popular anonymous messaging apps. It didn’t take long for critics to turn on Sarahah as a potential hotbed for cyberbullying and other online abuse, reflecting similar criticism of previous anonymous messaging apps. Critics have specifically pointed out that Sarahah and other similar apps offer a consequence-free environment where users can send anonymous messages that could be perfectly innocuous, or incredibly hurtful.

The tbh app seems to have been built as a potential answer to the criticism of its predecessors. It doesn’t appear that tbh users have much of an opportunity to slander their peers, as the app’s creators have said that poll submissions to tbh are closely moderated for anything resembling harassment, and only a small percentage of the thousands of daily submissions actually go on to become tbh polls.

Connecting TBH app to Snapchat, Instagram, and Facebook

As with previous anonymous apps, tbh users have taken to moving their activity off the app and onto secondary, non-anonymous social apps, like Snapchat or Instagram. As Fortune reported over the summer, Sarahah users took advantage of Snapchat’s linking feature to add links to their Sarahah profiles to the snaps they send to followers. New York magazine noted in September that tbh users also regularly share polling results, including screenshots of the tbh compliments they receive, on secondary apps like Snapchat and Instagram.

On Monday, a Facebook spokesperson told Fortune that the company plans to allow tbh to continue operating as its own standalone app.

Is TBH on Android and iPhone?

As of now, tbh is still only available to download on Apple iOS devices, and not on Google’s Android operating system. The company behind the app has not indicated when tbh might be available to Android users, though the acquisition by Facebook suggests that wider availability is likely to come soon.