There are two types of firewall available to the home computer user. A hardware firewall is a device which sits between your computer and the internet. At home for example it could reside on a broadband router which is used to share your internet connection with a number of computers. One of the advantages of a hardware firewall is that it can be used to protect more than one computer at a time. For this reason hardware firewalls are deployed in corporate networks. For home users who own just one computer a personal firewall is more commonly used and more cost effective.

A personal firewall is a software application that monitors and can block the flow of data between the internet and your computer. The firewall is a key part of your computer security set up. It prevents hackers from gaining access to your computer using an internet connection.

Hackers gain access to your computer through open ports that are used by your computer to communicate with the internet. The most basic firewall programs, like Windows XP's firewall, monitor and can block inbound traffic by closing these ports. If theses ports are closed a hacker cannot access your computer directly via the internet.

More advanced firewall programs like products from ZoneLabs or Symantec also monitor and can block outbound traffic. This extra level of security is important and is worth investing in. For example, if malicious software like a Trojan Virus or spyware were installed on your computer without your knowledge the firewall would alert the user when it tried to connect to the internet and prevent it communicating with its host.

A firewall usually works at two basic levels. Firstly, packets of data are analysed based upon IP address and content to see whether they comply with a set of rules which a user can input to. The second level the data is analysed is at the application level. The firewall determines whether an application can send and/or receive data and the port which it should be communicating through.

The firewall learns through continuous interaction with the user. It seeks user approval from programs when they first come in to contact with the firewall. Most firewalls also allow the user to allow or block applications through a stored list of program which can be accessed through the firewalls user interface.

There are a number of sites which will help test your firewalls effectiveness. A number of these sites are run by security software vendors so it is recommended you test using an independently run site to double-check any results. One of the best independent test sites is run by The Gibson Research Corporation. They offer a free test called Shield Up! which can be found at their website - http://www.grc.com. The test checks a number of well-know and vulnerable ports on your computer and then provides some useful additional information to help improve your security while online.

It is important to remember that the firewall is only part of your computer security and does not negate the need for a good anti virus solution, a spyware removal tool and a degree of caution / common on sense on the type of websites a user visits. For example, the firewall will not scan for viruses or remove them from your computer.

Richard Rogers is a owner of a number of computer related sites. One of his sites offers Free Computer Help for Windows XP Users and has just launched his new Registry Cleaner Blog.