Those facebook 'like' and 'share' buttons you see on a huge number of websites also interact with their systems. You don't have to be signed in, nor do you hav

Those facebook 'like' and 'share' buttons you see on a huge number of websites also interact with their systems. You don't have to be signed in, nor do you have to actually click them. They record your visit to the site, thus track you all over the web and build shadow profiles with your web visits, even if you don't have a profile. https://en.wikipedia.org/wiki/Facebook_like_button#Tracking https://en.wikipedia.org/wiki/Facebook_like_button#Tracking