In Mac OS X, how do I enable or disable the firewall?

Mac OS X includes an easy-to-use firewall that can prevent potentially harmful incoming connections from other computers. To turn it on or off:

Mac OS X 10.6 (Snow Leopard)

1. From the Apple menu, select System Preferences... . When the System Preferences window appears, from the View menu, select Security.
   
   
2. Click the Firewall tab.
   
   
3. Click Start or Stop to enable or disable the firewall, respectively.
   
   
4. To configure the firewall, click Advanced... . In the sheet that appears, there are a number of options:
   
   
   • For the strictest option, check Block all incoming connections.
   • Check Automatically allow signed software to receive incoming connections to allow digitally signed applications access to your network without prompting.
   • Click Enable stealth mode to have your computer ignore pings and similar software that attempts to discover your computer.
   • Use the plus and minus buttons to add and remove applications from the firewall. When added, you can either allow or block traffic to them.
   
   Click OK to save your settings.

Mac OS X 10.5 (Leopard)

1. From the Apple menu, select System Preferences... . When the System Preferences window appears, from the View menu, select Security.
   
   
2. Click the Firewall tab.
   
   
3. To configure the firewall, at the top of the window, click one of the radio buttons:
   
   
   • Set access for specific services and applications is the best choice for most users; it will block most incoming connections, but allow you to make exceptions for trusted services and applications.
   • Allow only essential services activates the firewall in its strictest mode.
   • Allow all incoming connections deactivates the firewall.

Mac OS X 10.4 (Tiger)

1. From the Apple menu, select System Preferences... . When the System Preferences window appears, from the View menu, select Sharing.
   
   
2. Click the Firewall tab.
   
   
3. Click the Start or Stop button to, respectively, activate or deactivate the firewall.
   
   If you would like to enable some incoming connections, you can make exceptions to the firewall (e.g., if you would like to share your iTunes music collection or if you have a web page on your computer that you'd like others to see). To add exceptions, check the boxes for services you'd like to enable under the Services and Firewall tabs.
   
   Because the firewall only blocks incoming connections from other computers, you usually won't have to enable ports for services on other computers you wish to access. For example, you don't have to allow Personal Web Sharing to access other web pages. There are exceptions to this rule, though, and if you find you are unable to access a specific kind of online service, try adding a firewall exception for it.
   
   Note: If the port or service type you wish to offer is not in the list, click New... under the Firewall tab, and then select Other. You must know the port number of the service to add it.

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