Where or How do those online sites get your employment information?

The online sites that charge a fee to view past employment history, where or how do they get this information. I thought employment history was somewhat confidential? Thanks|||Usually via your credit history. Every time you fill out a credit app you are asked where you work. That data goes on your credit history.|||if...you know what your doing...you can track people/information by an email...its all available free...if you don't want the world to know everything about you...never put your phone number on any document or send an email