Intego security notes benefits of outbound protection where malware attempts to connect to the Internet from an infected computer. By definition, all firewalls offer in-bound protection, and there are additional benefits in detecting and preventing malware from phoning home
QUOTE: The other day, we mentioned that the OS X application firewall provides only inbound protection. I imagine there are some of you who are wondering what exactly that entails, and more specifically, how that differs from what’s in Intego’s products. Well, guess no more! Here’s a handy explanation about the difference between incoming and outgoing firewall protection.
As you may imagine, inbound protection protects you from threats that originate outside of your Mac and try to get in. There are many types of automated or direct attacks that this type of protection is useful to combat, and this is the type of protection that OS X’s application firewall provides.
But arguably the more important component, from an anti-malware perspective, is outbound protection. Outbound protection alerts you to attempts to connect out from your machine. There are a lot of legitimate processes on your machine that do need to connect out (such as to get email, surf the web, get or update settings, etc.) but if there is unknown malware on your machine, you want to be able to prevent it from connecting out to send data or to alert its controller.