Activate the Mac OS X (10.5) Leopard Firewall

To activate the firewall in Mac OS X 10.5 (Leopard), follow these steps:

1. From the Apple menu, click System Preferences.
2. In the System Preferences window, click the Security icon in the top row. The icon is circled in white in the following graphic:
   
   
   

3. In the Security window, click the Firewall tab at the top of the screen.
4. If not already selected, click in the radio button to the left of Allow only essential services.
5. The window should now look similar to the following:

6. Click the Advanced button in the lower-right corner of the window.
7. If a check mark is not already present, click in the checkbox in front of Enable Firewall Logging.
8. If a check mark is not already present, click in the checkbox in front of Enable Stealth Mode.
9. The window should now look similar to the one below:
   

10. Click OK.
11. Close the Security window.