The casual user of Apple’s new operating system, Leopard, may not be aware that unlike in Tiger, the firewall is off by default. To turn it on, you’ll need to go to System Preferences/Security/Firewall tab.
This is a new interface which lets you specify firewall blocking by application rather than ports or services (unlike Tiger). There have been several reports that Leopard’s firewall does not behave like Tiger’s. In some cases, it appears that it is not blocking certain services indicated by the settings.
Stay tuned for ongoing information regarding Leopard’s firewall issues, including some other security issues arising from Leopard’s Screen Sharing capabilities.