A second look at the Mac OS X Leopard firewall

[Shawn Erickson]

Setting firewall access for services and applications
Mac OS X includes a firewall: a security measure that protects your  
computer when you’re connected to a network or the Internet. If you  
turn on a sharing service, such as file sharing, Mac OS X opens a  
specific port in the firewall for the service to communicate through.  
When you open the Firewall pane of Security preferences, any sharing  
services turned on in Sharing preferences, such as File Sharing or  
Remote Apple Events, appear in the list.

In addition to the sharing services you turned on in Sharing  
preferences, the list may include other services, applications, and  
programs that are allowed to open ports in the firewall. An  
application or program might have requested and been given access  
through the firewall, or might be digitally signed by a trusted  
certificate and therefore allowed access.

IMPORTANT: Some programs have access through the firewall although  
they don’t appear in the list. These might include system  
applications, services, and processes (for example, those running as  
“root”). They can also include digitally signed programs that are  
opened automatically by other programs. You might be able to block  
these programs’ access through the firewall by adding them to the list.

To add an application to the list, select “Set access for specific  
services and applications” in the Firewall pane of Security  
preferences, click Add (+) at the bottom of the list, and then select  
what you want to add. After the program is added, click its up and  
down arrows to allow or block connections through the firewall.

Blocking a program’s access through the firewall could affect the  
performance of other applications and services you use.
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