Look outside Facebook for information about how Facebook works. Facebook is annoyingly opaque when it comes to finding and fixing privacy settings. Rule of thumb, if an ad for a security or stalker app pops up on your wall, don't follow it. You have to dig to find and correct your Facebook settings, anything that is easy is a scam.

Those facebook "stalker "apps"? They don't work, so avoid them

"Considering how much information the normal Facebook apps can legitimately collect from your profile, it's wise to avoid apps that don't do what they claim (after all, if you can't trust a developer to market the app to you honestly, you can't trust him or her to use your data properly either). Don't fall for apps that pretend to tell you who's looking at your profile—they're not real!—and give into temptation with the unfriend scripts either. You're better off without them."