I was reading an earlier post regarding slot cards and a question came to mind. And this might have been asked and answered before.

What information is maintained on the slot card strips. Is it private information? I.E. Social Security Numbers and Names. Or just a customer id number?

The reason I ask this is with todays technology you can buy a card reader online with some software and read the information. My fear might be stupid but with the new trendy crime of identity theft, should this be a concern?