"Keeping your data private on Facebook" is kind of an oxymoron, but it's still nice that they let us play pretend with their security settings. Just remember that data you don't control is insecure by definition, and data on someone else's server (which is just about everything on the internet) is not under your control, no matter how much they might say it is.
Mokalus of Borg
PS - Also, expect that every server that lives long enough will get hacked.
PPS - This is not just a Facebook problem.