Both Windows and Macintosh systems have built-in firewalls. For the majority of personal computer users, these firewalls represent a good compromise between easy to use and security.
Enabling Windows Firewall
To Ensure Your Windows Firewall is Active
Enabling Macintosh Firewall
To Ensure Your Macintosh Firewall is Active
Note: If you decide to install a third party firewall on your computer, you should disable your operating system's built-in firewall. There should never be more than one firewall enabled on a single computer. Also, installing a third-party firewall can have unexpected side effects, including an inability to access the Internet. Be prepared to do a bit of troubleshooting if you choose to go beyond using the basic, built-in firewall that comes with your operating system.