A firewall protects your computer from Internet worms that exploit open ports and operating system vulnerabilities. Follow these instructions to activate the firewall on your Mac OS 10.4 (Tiger) computer.

1. From the Apple menu, click System Preferences.
2. In the System Preferences window, click the Sharing icon, highlighted in the graphic below:
   
3. In the Sharing window, click the Firewall tab.
4. If you see Firewall Off in the upper-left corner of the window, click the Start button below it to turn the firewall on. The window should now look similar to the one below:
   
5. Click Advanced in the lower-right corner of the window.
6. Check all three options (Block UDP Traffic, Enable Firewall Logging, and Enable Stealth Mode), if they're not already checked. The window should now look similar to the one below:
   
7. Click OK.
8. Close the Sharing window.