How does FlightAware's Flight Tracker Work?
 

I assume that Flightaware.com is a private company that provides a variety of flight information services. I also assume that the information required from their Flight Tracker service must come from FAA computers.

So how does Flightaware get the information? Do they have a contract with the FAA that allows them access to the FAA computers that has flight information for all aircraft, both commercial and private, that are connected to ATC?