Sen. Leahy has a Facebook pixel, invisible to users, that gathers user data of Facebook users who visit the site. (For a quick primer on what “pixels” do, visit Facebook’s resource guide on the data-gathering tool.)
That’s right, if you visit Senator Leahy’s campaign website, it’s likely your data, including your demographics and what pages you looked at on the site, have been placed into a custom data targeting audience by Leahy’s team.
Here is more, via @tedfrank. You will note that Leahy was one of the interlocutors who confronted Zuckerberg over the privacy issue.