Facebook FB, +0.20% wants to pay users to fork over their data, but privacy experts say the risks could outweigh the potential financial benefits.

The social-media giant this week announced Study, a “market research program” that will compensate willing users of Android, Google’s GOOG, +0.92% GOOGL, +0.95% operating system, in exchange for information about their phone-app use. Eligible Study participants must be 18 or older at the launch of the program and can opt out whenever they want to, the company said.

Users will be paid a flat monthly rate through their connected PayPal account. A Facebook spokeswoman declined to comment on exactly how much money users could make, and declined to provide information about the program beyond what was posted on Facebook’s website.

“ ‘I can imagine that if this app gets hacked, that opens up some pretty severe security vulnerabilities.’ ” — — Jennifer King, the director of consumer privacy at the Center for Internet and Society at Stanford University Law School

That app will collect a “minimum amount of information,” Facebook said, including which apps are installed on a person’s phone; how much time they spend using those apps; a participant’s country, network type and device; and potentially, which app features participants use.

Insights gleaned from the program, Facebook said, will help the company “learn which apps people value and how they’re used” and “build better products for the Facebook community.”

But some privacy experts and tech journalists are sounding the alarm over the company’s latest foray into “market research.”

Facebook’s track record with personal data is less than stellar

“We need more transparency from Facebook, and they have to go a lot of extra miles to prove that we can trust them because of their track record now,” said Pam Dixon, the executive director of the World Privacy Forum, a public interest research group. “Here’s the question: How much do you trust Facebook with your information?”

For starters, Dixon questioned whether any kind of independent review board had evaluated the Study program for its ethical and legal implications, and what standards the company had used to determine those. She urged Facebook to be transparent with that information.

A TechCrunch report earlier this year revealed that Facebook had paid users aged 13 to 35 up to $20 a month since 2016 in exchange for installing a “Facebook Research” app, which had harvested data on their web and phone activity. Apple AAPL, +1.02% yanked the app over a policy violation; meanwhile, a Facebook spokesperson maintained that “key facts about this market research program are being ignored” and that it hadn’t involved any secrecy or “spying.”

The company has also faced scrutiny over multiple data-centric scandals, including the revelation last year that the U.K. data firm Cambridge Analytica could have improperly harvested up to 87 million Facebook users’ personal information. In March, CEO Mark Zuckerberg vowed to build a “privacy-focused” platform in the future.

Facebook contends that it’s committed to transparency

In the Study announcement, Facebook emphasized its commitment to transparency. It maintained it would not collect information like usernames, passwords or content like photos and messages, and said it wouldn’t sell Study app information to third parties or use it for targeted ads. The company also stressed that it would inform users of what information they’d be sharing, how it would be used and how the app works, all prior to their providing any data.

Jennifer King, the director of consumer privacy at the Center for Internet and Society at Stanford University Law School, said she was glad that Facebook had made explicit the tradeoff between consumers sharing their app use and being compensated for it.

But she also raised the concern that Study would allow Facebook to build even more market power in terms of consolidating its position as an advertising platform. Facebook is expected to claim 22.1% of the U.S. digital ad market in 2019, according to eMarketer, second only to Google. And the company makes nearly $30 in ad revenue per user in the U.S. and Canada, its latest earnings report shows.

“It’s really easy to look at the consumer level and say, ‘Hey, I’m getting paid for this; why not?’” King said. “But this is a level of swooping in to observe how people are acting that I think is an interesting power play, and I’m just concerned that it adds more leverage to Facebook’s power as an ad platform that’s not positive for the open marketplace.”

“ People who use health-related apps, communicate with their minor children using apps like Snapchat, or handle financial dealings through apps, may want to think twice about jumping on board with Study. ”

Even the names of apps can reveal sensitive information

Dixon warned that even the names of apps, like ones related to pregnancy, weight loss or other health conditions, could reveal sensitive information about a user. King agreed that basic app data can “still give somebody a pretty deep view into your daily life.”

People who use health-related apps, communicate with their minor children using apps like Snapchat SNAP, -4.13% , or handle financial dealings through apps, may want to think twice about jumping on board with Study, Dixon said. King also pointed to personal tracking apps related to periods, fitness, food and meditation, and suggested it would be preferable to have the option to opt out of Study monitoring activity on certain sensitive apps.

She had security concerns, too. “I can imagine that if this app gets hacked, that opens up some pretty severe security vulnerabilities,” King said.

“Our activities on our [phones] are extremely revealing, and some apps leak a lot of data — I think this has been unambiguously documented,” Dixon agreed. “So we’ve got to really be careful of when we say yes to a deep marketing study.”

Facebook will first launch Study in the U.S. and India, two of its biggest markets, then expand its availability to other countries with time. The company will recruit people by running ads, which then allow them to register and receive an invitation to download a “Study from Facebook” app in the Google Play store. The crowd-testing company Applause, a longstanding Facebook partner, will handle registration, compensation and customer support.

A Facebook spokeswoman did not immediately return a request for comment on how the company planned to prevent hacks or data breaches involving Study.

For King, it boils down to one fundamental question. “It’s one thing to let Facebook track what you do on Facebook,” she said. “Do you really want them observing everything you do in the portions of your life?”