Start the Built-in Firewall in Mac OS X (v. 10.2 or higher)

1. Pull down the Apple icon in the top left corner of your Desktop

2. Select System Preferences from the menu.

3. Under the category Internet & Network click on the Sharing icon.

4. Make sure the Firewall tab is selected.

5. Click the Start button to enable the built-in firewall in your operating system.