How to enable or disable the built in Mac OS X: Leopard firewall.

1. Open System Preferences.

2. Open Security under the Personal section.

3. Click the Firewall button.

4. Do one of the following:

• Select Block all incoming connections to enable the firewall to block all incoming connections. Certain programs may not function with this setting though.
• Select Limit incoming connections to specific services and applications, then click the arrow next to Services to expand the list of services and then use the menu to the right of each service to allow ir disallow connections. You can do the same with Applications.
• Select Allow all incoming connections to disable the firewall.

5. Close System Preferences when you’re finished.