I mean, these machines, Stuxnet is a Windows virus.
Nimda (2001), named Concept Virus by its author, one of the first multi-vector Windows viruses.
I remember Windows viruses existing for Windows software that only existed in beta-format and available to developers.
As well, the first released models came with a Windows virus.
How can a Windows virus end up on an iPod?
A Windows Phone 7 antivirus could be scanning for Windows viruses.
And with a few exceptions individual Windows viruses aren't terribly widespread, just the sheer number of different ones makes infections common across the board.
So most Mac AV software spends 99% of its time scanning files for Windows viruses.
And no, the Intel chip does not make a Mac vulnerable to Windows viruses.
The company has managed to ship a limited number of GPS devices for cars containing not one but two Windows viruses.