Protect MacBook with Its Firewall

When you are using a known network to access the Internet, it should be equipped with its own firewall or Network Address Translation (NAT) protection to prevent computers you do not control from being able to see or access MacBook. However, if you are not sure about how much protection a network provides, such as when you are connecting to a network in a public place, you should use the Mac OS X firewall to block attempts to access MacBook from the Internet.

You might have to tweak the firewall a bit to be as secure as possible while still allowing you to do what you want.

Protect MacBook with Its Firewall

Open the System Preferences application.

Click the Security icon.