Facebook's tentacles stretch out across other websites and services, into the various apps you're using on your phone, and to the places you physically visit in the real world-especially if you decide to check in on Facebook while you're there.
It won't come as much of a surprise that Facebook tracks you on its platform-that's why it can resurface your birthday photos from five years ago-but you might not yet realize the scope and the depth of its tracking all across the internet.
