A firewall can protect your computer against hackers and other security attacks. The latest versions of Windows and the Macintosh operating systems have built in firewalls.
Note: The first time an application launches after turning ON the firewall, Windows may ask if you want to Block or Unblock the application. To allow the application to continue without further notifications, click Unblock.
Most Linux systems have a built in firewall that is both powerful and complex. An easy way to get a firewall configured on almost any Linux distribution with the graphical interface Gnome is to install Firestarter, an Open Source Linux firewall program. There are many other methods and guides available for configuring Linux firewalls. Search Google for instructions for your Linux distribution.
If you don't have Windows XP SP2, Zone Labs has a free basic firewall for individuals.
ZoneAlarm is free for individual and not-for-profit charitable entity use (excluding governmental entities and educational institutions). You can use it on your personal computer, but not on computers owned by the University.