The Leopard firewall will break World of Warcraft. I posted this on the "Leopard Firewall Criticized" thread, but I think it bears repeating if any of you play WoW. You can read about this bug here at the WoW forums. In short, one of the Blizzard support team wrote: "I was able to reproduce one instance of this problem internally. When I put the WoW game executable (application) in the Firewall config dialog where you can "set access for specific services and applications", the OS changes something about the application contents and then the signature check at login fails because the bits have changed. The OS has added a new file "CodeResources" into the application bundle, and also made some change to the executable itself, causing the checksum to no longer match what the server expects. My advice until we get this sorted out would be, don't mess with the Leopard firewall and do not put any of our applications on the special treatment list that the firewall panel provides. Additional info: if you have no backup copy of the WoW executable, you will probably need to reinstall to get it running again. Once you get to that point I would make a backup copy of the WoW application using Duplicate or (dare I say it) Time Machine, so this issue can be resolved quickly should it come up again."