How computer firewall works
Firewalls monitor all the communication between your computer and the Internet. computer firewall knows what kind of communication are allowed to flow in and out. They know this because they have something called an "access control list" - a list of rules that specify precisely what kinds of communications are allowed and what kinds are blocked. The computer firewalls made for the consumer market are usually preconfigured to offer maximum protection right out of the box. The configuration required to facilitate communication between two computers in a home network makes them highly vulnerable to attack from any computer on the Internet. Whether the firewall is a hardware device connected to your network, or a software program in your computer, a computer firewall will automatically block all unwanted network communication from the Internet, while at the same time permitting any legitimate communication that you need to use your computer.
Type of computer firewall
There are two principal types of computer firewall: hardware and software. A hardware computer firewall is a device connected to the network in such a way that all communications between any computer and the Internet must pass through the firewall and be examined to see whether they should be discarded or allowed to pass through. A software computer firewall is a program that runs on a computer and performs the same type of examination of network communications that a hardware firewall does. But where a hardware firewall can protect all of the computers on a network, a software firewall only protects the computer it is running on.
Things you need to know
Running multiple software firewalls is unnecessary for typical home computers, home networking, and small-business networking scenarios. Using two firewalls on the same connection could cause issues with connectivity to the Internet or other unexpected behavior. One firewall, whether it is the Windows XP Internet Connection Firewall or a different software firewall, can provide substantial protection for your computer. If your computer is not protected when you connect to the Internet, hackers can gain access to personal information on your computer. They can install code on your computer that destroys files or causes malfunctions. They can also use your computer to cause problems on other home and business computers connected to the Internet.
A Firewall helps to screen out many kinds of malicious Internet traffic before it reaches your computer. Some firewalls can also help to prevent other people from using your computer to attack other computers without your knowledge. Using a firewall is important no matter how you connect to the Internet - with a dial-up modem, cable modem, or digital subscriber line (DSL or ADSL). So it is wise to turn on the Windows Internet Connection Firewall for all computers in your home network. This helps prevent the spread of viruses or worms across your network if a computer is infected. A computer on the network could become infected through a separate Internet connection, such as one on a laptop that is used on your home network and on public networks.
Or a virus could be introduced to a computer on your network by way of e-mail or software installed from a CD or floppy disk. If you have more than one computer in a home or small-office network, you should protect every computer in the network. Turning on Windows Firewall or another firewall on every connection will help prevent the spread of a virus from one computer to another in your network if one of your computers becomes infected. However, if you open an infected e-mail attachment, the firewall won't block it and it can infect your computer. You should install an antivirus program as well.