In 2013, Facebook bought an Israeli app developer called Onavo, whose service helps consumer protect their mobile data while browsing. Now, the company has told legislators that it does not connect data from Ovavo to individual users’ Facebook profiles, while acknowledging it does use Onavo data to see what people are doing in other products and improve its own products accordingly.

Congress asked Facebook about Onavo in written questioning following CEO Mark Zuckerberg’s congressional testimony in April, which came in response to the Cambridge Analytica data-sharing scandal. On Monday, the company submitted hundreds of pages of answers to those questions.

Legislators wanted to know if Facebook uses traffic data collected from Onavo to “monitor the adoption or popularity of non-Facebook applications.” They also asked whether Facebook has used Onavo data in deciding whether to acquire companies or develop a particular product, and whether it links Onavo traffic information to profile data from its core services, “including for analytic purposes.”

In its response to Congress, Facebook said it “does not use Onavo data for Facebook product uses, nor does it append any Onavo data or data about individuals’ app usage to Facebook accounts.”

However, while personal information isn’t used, Facebook does look at Onavo’s broad data sets to see what types of products are popular and how customers are using them.

The company said it tells Onavo customers on the first screen they see that the product is owned by Facebook and that Facebook uses what it learns to help improve its offerings.

“People must tap a button marked ‘Accept & Continue’ after seeing this information in a full-screen interstitial before they can use the app,” Facebook said.

The company said that in both the iOS and Android apps, “we communicate repeatedly and up front” that Onavo is part of Facebook and what that means for how data is used.

The Wall Street Journal reported in August that Onavo data helped inform Facebook’s biggest acquisition ever, its $19 billion purchase of secure messaging app WhatsApp. It also helped Facebook shape its live video strategy in response to moves by Twitter, and figure out how to revamp Instagram to compete with Snapchat, the Journal reported.

—CNBC’s Arjun Kharpal contributed to this report.