Why have a code name when you are going to tell everyone?

I thought code names were supposed to be code names-- designed to mislead or confuse someone who is listening in with ill intent.

So why is it already out what the Secret Service names are for the Obamas and Bidens?.

If they are going to publicize the names then what is even the point of having them?

Now granted, they may very well be just public code names while they actually use other code names (in fact I'd say this is highly probable) but there still isn't any point in publicizing even the first set of names (then someone who figures them out will think they actually found something.)