I have talked about firewalls and how it is configured to secure your computer from malicious access but it seems that I have failed to even mention the one that comes bundled with Ubuntu, Firestarter. Firestarter is an easy to use firewall with the following key features:

• Open Source software, available free of charge
• Easy to use graphical interface
• Suitable for use on desktops, servers and gateways
• Enables Internet connection sharing
• Allows you to define both inbound and outbound access policy
• Option to whitelist or blacklist traffic
• Sets up DHCP for a local network
• Real time firewall events view
• View active network connections, including any traffic routed through the firewall
• Advanced Linux kernel tuning features

Whilst Ubuntu comes with this pre-installed, here is a good how-to in setting it up properly.

Image from Flickr:spielzimmer.