Access Denied: Press Privacy Settings under Account and go to Applications and websites. From there, click Edit your settings, and then Info accessible through your friends. There, you'll find a detailed table of items you can deselect from sharing when your friends allow apps to access your profile information; for full privacy, deselect everything (recommended).
The Ultimate Security: Delete the Account
Deleting your Facebook account entirely is a draconian step, but it may be worth considering if you feel you've outgrown the usefulness of Facebook, or have simply changed in outlook. All those drunken or injudicious frolics--or simply the need to adopt a professional persona in public--may mean you need to wield the ax over your Facebook account.
The problem is, you can't--at least not without doing some digging. You can only deactivate your account, which makes it, dormant so to speak, from your Account Settings page. Your profile is still there, in hibernation, still available to Facebook.
Deep-sixing Your Facebook Account: Be warned--this process takes 14 days, and you cannot use your Facebook account in any way once initiated. The link to permanently delete your Facebook account is buried deep in Facebook's Help pages, so we found it for you. Request that your account be deleted here.
Press Submit. Fill out the resulting form, then press OK. Leave the site, never to return.
Facebook is great fun, but ultimately you are responsible for staying safe and secure. And although Facebook has its responsibilities too, the onus is on individual users to understand how the privacy and account settings work, to apply Facebook's privacy controls, and to regulate their own behavior. Even if Facebook should, hypothetically, be sanctioned for losing user information--for letting it get into the wrong hands--that will be little comfort if you are one of the victims.