It seems as though the mass adoption of Mac OS X Leopard is bringing Apple more than publicity and sales. The German security experts at Heise Security and security blogger Rich Mogull tested OS X Leopard out for themselves, and found some serious problems. The OS X Leopard firewall works by signing applications that aren't already signed by Apple, so that they are given the go-ahead by the firewall. Unfortunately, when a program changes, that go-ahead disappears. Skype is one of those programs that changes itself, and so it comes as no surprise that Skype users are reporting trouble getting Skype to work on their Mac OS X Leopard computers. World of Warcraft also has this problem, though it's not entirely understood why. World of Warcraft forum members report that reinstalling the game clears the bug right up.