90 percent were given access to information they didn't need in order for the app to function. So when you sign up to find out what sitcom star you most identify with, the makers of that poll now have access to your personal information. It's anybody's guess where it goes from there.
Social networking is all about sharing, so something you think is in confidence can easily be shared and then shared again, and before you know it, someone you don't even know has access to something private. "When in doubt, leave it out" is a good motto to follow. And always remember that anything you share has the potential to be leaked in some way.