You don't need any 3rd party antivirus/antimalware software to protect Mac OS X from malware. No viruses exist in the wild that can run on Mac OS X, and there never have been any, since it was released 10 years ago. The handful of trojans that exist can be easily avoided with some basic education, common sense and care in what software you install. Also, Mac OS X Snow Leopard and Lion have anti-malware protection built in, further reducing the need for 3rd party antivirus apps.