Facebook is pushing its data-tracking Onavo VPN within its main mobile app.

Onavo Protect, the VPN client from the data-security app maker acquired by Facebook back in 2013, has now popped up in the Facebook app itself, under the banner “Protect” in the navigation menu. Clicking through on “Protect” will redirect Facebook users to the “Onavo Protect – VPN Security” app’s listing on the App Store.

We’re currently seeing this option on iOS only, which may indicate it’s more of a test than a full rollout here in the U.S. It’s unclear what percentage of Facebook’s user base is seeing the option, or which markets may have had this listing before, as there’s been little reporting on the feature.

We do know this is not the first time Onavo’s Protect has shown up in Facebook’s app – it was spotted before in 2016 in the UK.

Marketing Onavo within Facebook itself could lead to a boost in users for the VPN app, which promises to warn users of malicious websites and keep information secure – like bank account and credit card numbers – as you browse. But Facebook didn’t buy Onavo for its security protections.

Instead, Onavo’s VPN allow Facebook to monitor user activity across apps, giving Facebook a big advantage in terms of spotting new trends across the larger mobile ecosystem. For example, Facebook gets an early heads up about apps that are becoming breakout hits; it can tell which are seeing slowing user growth; it sees which apps’ new features appear to be resonating with their users, and much more.

This data has already helped Facebook in a number of ways, most notably in its battle with Snapchat. At The WSJ reported last August, Facebook could tell that Instagram’s launch of Stories – a Snapchat-like feature – was working to slow Snapchat’s user growth, before the company itself even publicly disclosed this fact.

This past fall, Facebook snatched up the teen compliment app tbh, and quickly integrated a similar Q&A feature into its social network soon after. This all took place before Tbh had truly established itself as a new social network. It wasn’t clear at the time if it was the next big thing, or just a flash in the pan. (It appears to have been the latter.) Onavo’s insights into Tbh’s fast rise and heavy engagement likely gave Facebook a heads-up.

The Onavo app today has more than 33 million installs across the iOS App Store and Google Play, according to data from Sensor Tower. Around 62 percent of those from Google Play – which could be another reason why Facebook is giving Onavo a push on iOS. The U.S. is currently the app’s largest user base, followed by India and Brazil.

Onavo’s app store description explains that it’s “a part of Facebook,” and that it’s used to “improve Facebook products and services, gain insights into the products and service people value, and build better experiences.”

However, it’s not likely that all Onavo users understand they’re actually feeding Facebook the information that allows it to take on any challenger to its social networking empire. (That empire also includes WhatsApp and Instagram as well as smaller acquisitions like tbh and MSQRD).

Facebook hasn’t yet offered a comment on the new addition of Onavo to its main app, but we’ll update this post if one is provided.

This would not be the first time Facebook has integrated one of its other mobile apps into Facebook itself. The company earlier made it easier to launch Instagram through a new Facebook feature, and it has tested and rolled out various WhatsApp integrations, too.