The problem with Facebook is all the apps. You have to be VERY careful which apps you authorize, and many users are not. A rule of thumb I use is if the app doesn't have at least three out of five stars, it ain't getting in the door. If there are mis-spellings in the app description, no-can-do. If I have any reason to doubt it's legit, it goes on the Block list.
Unfortunately, many users just authorize stuff left and right because it promises boobies, a "shocking video," free points for Mafia Wars, a Dislike button, or what-have-you.