"Like" a page about a particular disease, for instance, and marketers may begin to target you with related products and services.

Facebook may be collecting sensitive health data in far more insidious ways as well, however, including tracking you when you're on hospital websites and even when you're in a personal, password-protected health information portal like MyChart.1

It does this via pixels, which may be installed without your knowledge on websites you visit. They can collect information about you as you browse the web, even if you don't have a Facebook account.

Meta Pixel Found on Hospital Websites
In particular, the Meta Pixel is a piece of JavaScript code that developers can add to their website to track visitor activity.2 According to Meta:3

"It works by loading a small library of functions which you can use whenever a site visitor takes an action (called an event) that you want to track (called a conversion). Tracked conversions appear in the Ads Manager where they can be used to measure the effectiveness of your ads, to define custom audiences for ad targeting, for dynamic ads campaigns, and to analyze that effectiveness of your website's conversion funnels."

Even hospitals are opting into the data trackers, as evidenced by an investigation by The Markup, which tested websites from Newsweek's top 100 U.S. hospitals. Facebook's Meta Pixel was found on 33 of the websites, sending Facebook information linked to an IP address, which identifies individual computers and may be traceable back to an individual or household.