[G4] Virus and Mac OS X?

[Kristen]

I recieved an email damon message this morning stating all the messages that 
bounced due to closed mailboxes and do to a virus. So I have to wonder where 
this virus came from? I thought a Mac OS X can't run a virus since it's 
Darwin linux. At least at the core. I know it can't be my Linux box since it 
will not run a virus at all. That leaves the Windows XP my son uses, but the 
emails are returned at my email addy. 

So let me ask, Will the Mac OS X (Tiger) run a virus and automatically run the 
email program? BTW, the Mac was in sleep mode. I don't believe it's the Mac. 

Thank you all!!

Kristen