Some Leopard (opens in new tab) users have reported facing problems when using Skype or Online Games like World of Warcraft.
German-based Heise Security points its finger to Mac OS X Leopard's firewall as the root of all the problems with the issue originally found by German users back last week.
Unlike Windows Operating Systems, Apple users cannot change program privileges which can cause problems with applications like Skype.
The popular VoIP software and many legitimate ones need to change their code as they run which causes Leopard's firewall to raise a flag and block them because it mistakenly assumes that a malware has changed the size of the running app.
As Heise (opens in new tab) puts it, "The background to all this is that, in contrast to Tiger, the firewall in Leopard no longer operates at the packet level but rather it works with applications, to which it permits or denies specific network activities."
Signature-based defences have been criticised by security companies like Tier-3 for being easily fooled by decade old scripts.