A firewall acts as an bridge between you and the Internet. It looks briefly packets going in and out of your system, and offers each of the thumbs up or thumbs down verdict. (Pass or block). This measure can prevent intrusion attempts within your system. Firewalls come in two types: Equipment and software. Software firewalls run on the system and works in the background, monitoring your connection. It possibly called "Personal Firewall". Hardware firewalls are separate boxes that make the firewall, without taking the system resources. Almost all routers have at least the basic functions of a firewall.