is it true that a Mac cant get infected in any way off the internet?
Mac OsX 10 through OsX 10.6 are absolutely vulnerable to net viruses and malware. Can't speak for OsX 10.7 - I'm not even sure it's been released to the public yet.
Most nasties are designed to get
Windows based computers - they're the vast majority of machines out there. It's as simple as an ROI calculation - why design software to target (at best) one or two percent of your "audience" when you can get darn near a hundred percent by goin' for
Windows? The protection offered by the Mac system is, basically, that you're a minor fraction of the internet traffic out there, so the nasties aren't aimed at you.
As the Macs have become more popular over the last few years, I've seen more and more stuff pop up to target them. Had to nuke some stuff off my own machines!
Diligence and caution are the only real defenses you can deploy. For every AntiVirus program out there, there's a thousand folks trying to defeat it!
Sorry to go off post on my first (post)!