Firewalls What are firewalls? Firewalls are a way of protecting your computer by keeping out unwanted "intruders." A firewall should isolate your computer from the Internet using a safeguards that inspect each individual "packet" of data as it arrives at either side of the firewall — incoming  or outgoing from your computer — to determine whether it should be allowed to pass or be blocked. In fact, it is believed that firewalls should be part of all computer software whether networked on a home system that will be online. Intrusions detection software is slightly different but the firewall concept will be dealt with here. Who should firewall? If has been suggested that in the near future, firewall software will be part of most computers you buy. If you connect via a dial-up connection, you are only online and vulnerable while you have that connection active. When you hang up, your computer is again isolated from any threat. However, if you have a cable connection or any of the other available connections where you do not have to dial-up, that means you are connected 24 hours daily and vulnerable to anyone that wants in your pc. You don't necessarily have to be there, remember, it's connected 24/7. If you are one of these users, operating without a firewall is like going to bed with all your doors and windows wide open.  How do firewalls and internet connections work? Actually, all connections to the internet are done with small packets of information. As these packets are sent from one machine to the other, the two machines agree on the connection and then check each other to see if the packets they sent are being received accurately on the other end.every Internet packet must contain a destination address and port number. So that the receiving computer knows who sent the packet, every packet must also contain the IP address and a port number of the originating machine. In other words, any packet travelling the net contains — first and foremost — its complete source and destination addresses.  Since the firewall software inspects each and every packet of data as it arrives at your computer — BEFORE it's seen by any other software running within your computer — the firewall has total veto power over your computer's receipt of anything from the Internet.  A port, opening on your computer to receive and send data, is only "open" if the first arriving packet requests the establishment of a connection and is answered by your computer. If the arriving packet is ignored, that port of your computer will effectively disappear from the Internet. No one and nothing can connect to it! This is the firewall theory--you can accept or reject data from anywhere. In effect, you can "filter" out the other computers that you don't want to see your computer. An excellent resource for even more detailed information can be found at the Gibson Research Corp. along with some useful tools to see how secure your own computer is, with or without a firewall. Firewalls available for your computer- An excellent computer program called the Digital Duo airs weekly on many tv stations. More info can be found at their site, DigitalDuo. One of their offerings dealt with firewalls and their page from that episode called "Buildin' a Firewall contains more in-depth info on the following firewalls with comments and recommendations for each. They also rate each. That specific episode can be found with a click here. One company that makes an excellent firewall is Zone Alarm located at their web site at Zone Labs.com   I use Zone  Alarm with commendations to the company.Not only is this considered one of the best for the home user but it is free to download. There is also a "professional edition" that has more options, requires a fee, and is designed more to business or professional applications. They also have many useful pages of information and resources on computer security. Norton, a well-known company in computer security has a product called Internet Security 2001 and can be found at their web Norton web site. Network ICE is another firewall product called BlackICE Defender. While being a very good product, it requires, according to those who use it, a little more "techie" experience in getting used to it. It is excellent and minimally priced.  Shields Up is from the folks at GRC and is an excellent product also. The site has many useful tests you can run also. Summation- A firewall is not difficult to load, set up, and use. It is a highly recommended practice in cyberworld today.