A firewall can protect your computer against hackers and other security attacks. The latest versions of Windows and the Mac operating systems have built in firewalls.
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.