What is a personal firewall?
A personal firewall is another way to protect your computer. You may not be aware of it, but your computer is listening on a large number of ports. These ports are affiliated with specific services that your computer either uses or provides. For instance, in order for you to look at this web page, your computer is allowing tcp traffic on port 80 (this can be changed, but the default port for unencrypted http traffic is port 80). If you were to block port 80, you would be unable to view http web pages. However, certain programs shouldn't need to communicate via that port. For instance, Solitaire should not need to communicate across port 80. If it attempts to do so, that might be a sign of a problem with your system. In addition to monitoring communications from your computer, a good firewall will also monitor communications directed towards your computer.
So what we need is a way to identify what programs are communicating via the network, and possibly what ports they are communicating over. This is what a personal firewall will do.
Where do I get a personal firewall?
If you have installed Service Pack 2 for Windows XP, you already have a personal firewall. You can access it by opening the Security Center (Start -> Settings -> Control Panel -> Security Center). If the personal firewall is active, you will see an image like this:
If your firewall is turned off, you should turn it on. To do so, click on Windows Firewall under Manage security settings for: and then click On (recommended) and click OK. The firewall graphic in the Security Center should now match the one above. Close the Security Center.
If you don't have Windows XP with Service Pack 2, or you would like to install an additional firewall, there are several firewalls that are available for free personal use. Your options for free for personal use firewalls include Zone alarm [link outside of LUC] by Zone Labs [link outside of LUC], Sygate Personal Firewall [link outside of LUC] by Sygate [link outside of LUC], or Kerio Personal Firewall [link outside of LUC] by Kerio Technologies [link outside of LUC]. Please note that these free versions will often attempt to get you to upgrade to a paying version. You do not need to upgrade in order to receive protection through these firewalls.
How do I configure my personal firewall?
If you are using a firewall other than the firewall built into Windows XP Service Pack 2, please follow the directions from that vendor to configure the firewall. To configure the Windows firewall, first make sure that it is enabled as described above. For most users, this is the only step you will need to take. If you are using your computer as a server, such as a web server, you may need to perform additional configurations to allow incoming connections. If that is the case, you may need to manually allow certain ports through your firewall. Information on how to do so can be found on Microsoft's site [link outside of LUC].