Facebook reportedly withdrew its free mobile VPN app Onavo Protect from the Apple Store last week after Apple expressed concern over data privacy violations.

According to the Wall Street Journal, Facebook uses various analytical abilities built into its VPN app — originally acquired from an Israeli analytics company Onavo — to extensively monitor and map users’ behavior beyond what is relevant to Facebook’s own apps. Apple reportedly told the Menlo Park, Calif.-based social media company that this is a violation of its iOS developer agreement.

Additionally, Apple reportedly informed Facebook it also failed to comply with new privacy rules that the Cupertino, Calif.-based tech giant established this past June. Among other stipulations, these rules state apps that collect user permissions in order to access contact lists and photos are prohibited from creating databases populated with that information or selling the data to third parties.

The WSJ further reported Facebook voluntarily removed its app after Apple officials suggested this specific action in a face-to-face meeting earlier this month. Apple reportedly told the WSJ in a statement that its developer guidelines clearly forbid apps from collecting information on users’ other apps for analysis or marketing purposes.

“We’ve always been clear when people download Onavo about the information that is collected and how it is used,” said a Facebook spokesperson in response to an SC Media inquiry. “As a developer on Apple’s platform we follow the rules they’ve put in place.”

But some VPN experts weren’t particularly forgiving in their assessments.

“Facebook is by far the organization with the most amount of data on users the world has ever seen. Their appetite is so big that they want to know what users are doing outside their app, and offering a VPN service is like laughing in our face,” said Ariel Hochstadt, co-founder of vpnMentor. “With so many organizations trying to sell our identity, it comes at no surprise that VPN sales increased 165% in 2018, according to a recent analysis we conducted.”

“Big data is a huge industry and with free applications, most likely you are the product,” added Robert Madisalu, chief researcher at TheBestVPN.com. “If we’re talking about VPNs, then probably the most expensive ones are the safest, since they don’t need the big data money. Free is not always the best, as people tend to believe.”

Peter Zaborszky, founder of BestVPN.com (not to be confused with the aforementioned TheBestVPN.com), said that when Facebook acquired Onavo, “many users were not aware” that the information it collected was being used to improve Facebook products and services, and gain insights into industrial products. “On one hand, Onavo marketed a VPN product designed to improve the privacy and security of its users. And on the other, it did not make clear that, in turn, the VPN provider was able to gain access to the provided personal information” — a capability that Facebook reportedly leveraged to monitor the performance of competing apps,” Zaborszky continued.

Those who already have already downloaded Onavo on their iPhones will still be able to use it, but they will no longer receive updates from the Apple Store, the WSJ reported.