Macs are famous for being almost impervious to viruses, right? I downloaded a couple of zip files of programs. I've scanned the downloads with Norton (Norton says no problems found in compressed files), but... I'm afraid. Is this enough? When I open a zip file, I'm eventually going to also have to install a .dmg or an .exe file, right? Am I safe? Or is there something else I can do to be safe? Thanks for your help!