Facebook has a new way to make money off of your data—and, potentially, to learn more about you than it ever could before.

If you're a Facebook user, the company's machines already know all the things you've explicitly told Facebook over the years, like your name, age, email address, friends, likes, and interests. They also already know how you behave on Facebook, including which types of stories you're likely to click on and which friends' status updates you like the most.

Now they're beginning to learn more about how you behave when you aren't on Facebook. For instance, they have the ability to know whenever you visit a Web page that has a "like" button. For years Facebook insisted it wouldn't use this sort of data to track your activity for commercial purposes. Recently, it decided it might start doing that after all.