Closing Outpost Firewall's main window does not shut down the firewall. Its icon remains in the system tray.
There are two ways to shut down Outpost Firewall:
Right-click on the system icon to display the context menu. Select Exit and Shutdown Outpost. This closes the interface and stops the firewall so Outpost Firewall is no longer protecting your system.
When Outpost Firewall's main window is displayed, go to the File menu and select Exit. This closes Outpost Firewall's interface but leaves the firewall running in memory, blocking connections and banners, etc.
When Outpost Firewall is shut down, its icon disappears from the system tray indicating that the firewall is no longer protecting your computer.