Free firewall

You can block uninitiated and unwanted traffic, even while your PC is unattended or while you're not using your connection. You can also limit your exposure to attack by specifying which applications can access the Internet. This program includes four interlocking security services: a firewall, an application control, an Internet lock, and Zones.

The firewall controls the door to your computer and allows only traffic you understand and initiate. The application control allows you to decide which applications can and cannot use the Internet. The Internet lock blocks Internet traffic while your computer is unattended or while you're not using the Internet, and it can be activated automatically with your computer's screensaver or after a set period of inactivity. Zones monitor all activity on your computer and alert you when a new application attempts to access the Internet.

Download Zone Lab's Zone Alarm