An application firewall limits the access which software applications have to the operating system services, and consequently to the internal hardware resources found in a computer, much as a car firewall limits access of heat, or even fire, to the passengers of the vehicle. The reason that application firewalls are needed in today's internet and data-sharing world is that the other types of firewalls in existence do not control the execution of data, only of the flow of data to the computer's processor.