A firewall is a software program or hardware device that acts as a barrier between the Internet and your computer or networked server (a computer that "serves" multiple computers). A firewall prevents unauthorized access to your computer or server (by both software programs and unauthorized Internet users) and hides your Internet-connected computer from view. All information leaving and entering your computer must pass through the firewall. It ultimately helps keep hackers away from your personal and confidential information.
Even if you have anti-virus and anti-spyware software installed, you need a firewall. A firewall is the perfect complement to anti-virus and anti-spyware software, providing a key component of a multilayered security strategy.
Firewall protection is available from McAfee, it's built into Windows (you just need to enable it), and there are several free firewalls available. For affordable, worry-free protection we recommend Frontier Secure Computer Security.