content: Facebook makes shadow-profiles for people who don't have accounts, by collecting tertiary information and compiling your browsing habits through both third-party and internal trackers. Signing in with Google, to a website that has a "Like us on facebook!" button, is usually enough to pin-point your exact (IRL) identity. Even if you're super paranoid about that stuff, like I am, it's inevitable that some of your information gets leaked, from time to time, and this slow-drip of data is collected over the course of years. IP addresses, browser headers, ad-network IDs, etc. Any time you play a smartphone game with ads, it pulls said ads by sending your ID to the ad network to retrieve relevant ones. They know every time you're sitting down to take a shit and playing a quick round of angry birds. And they all share this information, freely, amongst themselves (Google, facebook, Microsoft, NSA, etc).