Best answer as chosen by user evaq: On Mac OS X
On Mac OS X, there's no need for a separate malware program. There really isn't on Windows if you avoid things like Internet Explorer, but that's another topic for another time.
For the most part, Apple has their own malware removal program baked into OS X, and it triggers automatically.
I also think you are confused. Retrospect is a backup program, and on the off chance they had expanded into including an AV product in the 10 or so years since I last used Retrospect, I checked and they still appear to be a backup only company.