Why do people try to get in your business at work??? What is the most polite thing to say to?

them...but I want them to STOP. It is really none of their business to know anyway. I have said things like.."well, it is NONE of my business to know anyway.".."i am sorry, that is personal." They just look at me?????.But they still try to get in one's business. How do I STOP THEM?? Haven't they heard of boundaries? geez! It frustrates me!!!