As you travel through the web, you’re likely to encounter Facebook Like or Share buttons, which the company calls Social Plugins, on all sorts of pages, from news outlets to shopping sites. Click on a Like button and you can see the number on the page’s counter increase by one; click on a Share button and a box opens up to let you post a link to your Facebook account.

But that’s just what’s happening on the surface.

“If those buttons are on the page, regardless of whether you touch them or not, Facebook is collecting data,” Oppenheim says.

Behind the scenes, every web page contains little bits of code that request the pictures, videos, and text that browsers need to display each item on the page. These requests typically go out to a wide swath of corporate servers—including Facebook—in addition to the website’s owner. And such requests can transmit data about the site you’re on, the browser you are using, and more. Useful data gets sent to Facebook whether you click on one of its buttons or not. If you click, Facebook finds out about that, too. And it learns a bit more about your interests.

In addition to the buttons, many websites also incorporate a Facebook Pixel, a tiny, transparent image file the size of just one of the millions of pixels on a typical computer screen. The web page makes a request for a Facebook Pixel, just as it would request a Like button. No user will ever notice the picture, but the request to get it is packaged with information.

…Facebook explains what data can be collected using a Pixel, such as products you’ve clicked on or added to a shopping cart, in its documentation for advertisers. Web developers can control what data is collected and when it is transmitted.

…“If you’re logged into Facebook with the same browser you use to surf the web, the company knows exactly who you are and the vast majority of the websites you visit,” Oppenheim says.

Even if you’re not logged in, the company can still associate the data with your IP address and all the websites you’ve been to that contain Facebook code.

…In materials written for its advertisers, Facebook explains that it sorts consumers into a wide variety of buckets based on factors such as age, gender, language, and geographic location. Facebook also sorts its users based on their online activities—from buying dog food, to reading recipes, to tagging images of kitchen remodeling projects, to using particular mobile devices.

The company explains that it can even analyze its database to build “look-alike” audiences that are similar to, say, Lil-Kick’s best customers.

How Facebook Tracks You, Even When Not on Facebook – Consumer Reports

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