What is a firewall?
A firewall is a software program or piece of hardware that helps screen out hackers, viruses, and worms that try to reach your computer over the Internet.
If you use a computer at home, the most effective and important first step you can take to help protect your computer is to turn on a firewall.
Windows 7, Windows Vista, and Windows XP SP2 or higher have a firewall built-in and turned on by default.
If you have more than one computer connected in the home, or if you have a small-office network, it is important to protect every computer. You should have a hardware firewall (such as a router) to protect your network, but you should also use a software firewall on each computer to help prevent the spread of a virus in your network if one of the computers becomes infected.
(If your computer is part of a business, school, or other organizational network, you should follow the policy established by the network administrator.)