About the only way to really be "safe" is use an extremely obscure operating system, that's built off of a random no name kernel. However good luck with anything of yours being compatible but at least it'll be safe... The whole illusion of Macs being safer then PC's is an example of this. Why because on a macro scale, no one uses Macs, so people who write viruses aren't going to waist there time on a minority OS, instead they're gonna try and get as much bang for there buck when it comes to there virus. Personally if I wrote viruses I'd make them specifically for Macs as i hate the company on more than one level and would aid in any way to there downfall, but that's just me (Not that I do, nor do I condone it, but still using it as a example to display my dislike in Apple). Secondly the people that right more complex viruses generally target companies, which again is dominated by PC's and in some cases a few flavors of *nix which generally are used to run servers, databases and what have you using OS's such as Red Hat, etc.
So moral of the story safety in the computer world = ambiguity