Leopard firewall problems

A few days ago I started to have an issue with Skype on Leopard. Skype worked fine for me on Leopard for a number of days and then stopped working. When I would try and start the application up, it would bounce in the doc a couple of times and then quit.

Due to time constraints I didn’t pay much attention to the problem for a couple of days but had to go back to figuring out the problem as I was scheduled to go to Germany for work. I wanted to use Skype to make inexpensive calls back to the family in the states while in Germany.

I started to research the problem and discovered that the problem was Leopard’s new application firewall. Leopard ships with its firewall disabled by default (thumbs down to apple for this one). While this in itself is bad, it gets worse. I had recently turned the application firewall on in Leopard and this was when Skype stopped working. Some research discovered that Apple is modifying application binaries when you set firewall rules against the application. What in the world was apple thinking?

I have been using a firewall on my Macs for a few years now called Little Snitch. Little Snitch alerts you when an application tries to send out data. This in conjunction with Apple’s standard firewall is a great way to protect your computer from applications phoning home, trojans, viruses, etc..

Another problem that I have seen with Apple’s new firewall is that it does not report on certain “Apple Related” activity. There is a nice writeup on this here.

More information on the firewall and application modification is here.