You may log on to Facebook because it allows you to share photos and get updates on your friends, but that’s not why it exists, and it’s certainly not why it is worth about half a trillion dollars.

Facebook’s value comes instead from all the information it gathers, and what that information is worth to others. It is, as privacy expert Zeynep Tufekci said in The New York Times this week, surveillance disguised as social interaction — Facebook takes your likes and comments and uses them to figure out what makes you tick, all so the company and its clients can sell you stuff.

According to The Times, Cambridge Analytica, a voter-profiling firm, acquired that information through subterfuge, then used it to create profiles on millions of American voters for the purposes of influencing their behavior.

The firm, which worked on President Donald Trump’s 2016 campaign, believed it could take a person’s Facebook activity, meld it with other available data, and discern a person’s personality traits, political leanings, mental health status, substance abuse history and more. They then could target those individuals with messages specifically designed to exploit their vulnerabilities.

It’s unclear if this works as Cambridge Analytica says it does, but it’s not the tailored targeting of voters that makes this story so concerning. After all, that’s not so out of line with what others are doing. Retailers, for instance, have every reason to use your digital fingerprints to figure out what it’s going to take to sell you your next pair of jeans.

No, the problem isn’t that a company wants our information, it’s that all our information is in one place. It isn’t that companies can track our web activity and browsing histories, but that so much of that activity takes place on a single site, and one whose business model is based on exploiting its users.

It would be nice to say that individuals should heed this as a warning to watch what they are sharing online, but that’s hardly realistic. Facebook, for many people, is the internet. It’s how they interact with friends, plan events, find deals, and read the news. It became so indispensable so quickly that most people don’t mind giving up what they see as a little privacy for the sake of convenience.

But data mining and profiling are becoming more sophisticated, and we may not realize how much we are truly giving up. Companies have always sought to understand their customers, but now they have a tool that spends all day and night sucking up and analyzing information. We are giving away a lot more about ourselves than we realize, and that information is just begging to be misused.

Trusting Facebook to act in the best interests of its users is not an option, particularly when its real customers are the companies that buy user information.

Cambridge Analytica, for instance, was reportedly allowed to access the Facebook information by claiming it was being used for research, a claim Facebook never tried to verify. When several accounts of the breach surfaced, Facebook originally denied it, even though they had identified the breach internally. The company has still not verified that Cambridge Analytica destroyed the information as requested, nor has it contacted the users whose information was compromised.

That is not something that can be solved with a new Facebook user agreement. We need a public policy response to privacy that takes into account the new realities of online life, and which can protect people’s rights with the same gusto Facebook has brought to harvesting personal information.