For unfamiliar terms, look in Matisse Enzer Glossary of Internet Terms.

A firewall puts a virtual wall between you and the hackers on the internet. It can be hardware or software. I don't have much experience with hardware firewalls, beyond routers which I'll discuss in the network portion, so I'll focus on software firewalls here. You see, when a computer is connected to the internet by broadband or telephone line, the connection is like a "super-highway" with thousands of lanes for the information to travel back and forth like cars on a real highway. These lanes of internet traffic are called ports. Your computer uses them to send information back and forth. Hackers use these ports to get into your computer if the ports are open. The ports can be open, closed, or stealthed. Often hackers use software to scan portions of the internet for vulnerable computers by looking for evidence of open or closed ports. You see, even if the ports or lanes for traffic are closed, when a hacker scans for them your computer or improperly configured router will return a message that the ports are closed. This confirms to a hacker a computer is there. They can then begin their attack against your computer. The firewall can stealth your ports so they do not respond as open or closed. The hacker won't even know your computer is connected to the internet. If they don't know your computer is there, they can't attack it. A firewall can manage the traffic letting you surf the web safely while keeping the hackers out. A good firewall will prevent bad traffic from getting in or out of your computer.

The program I recommend for this is ZoneAlarm. ZoneAlarm is a FREE, powerful software firewall. You can also buy ZoneAlarm Pro that has other security features. ZoneAlarm monitors all the traffic coming into and out of your computer. It recognizes the information you want to come in from the web like web pages so you can still surf the web, but stops hackers from getting in. It also monitors all out going traffic. If another program or trojan (malicious program like a virus) on your computer tries to send information to the internet, Zone Alarm will ask you if you want that program to communicate with the internet. You can set up rules so ZoneAlarm remembers which programs can communicate with the web and which ones cannot.

One note about software firewalls and home networks: it takes a little more configuration of the software to allow the computers on your home network to communicate with each other for file and printer sharing. You'll need to set up a "Trusted Zone" by specifying the IP addresses of the other computers on your network. Don't worry; the program is fairly easy to set up. If you have trouble, there is a great help file included, and I'd be glad to answer any questions.