Running Windows on a Mac as a virtual machine won’t protect your Windows installation from any viruses it would have otherwise gotten unless you take some other additional quarantining provisions.

*If the data your trying to protect is on the Mac (for example, you use e-mail on the Windows machine but keep critical business documents on the Mac partition), however, it is a little safer, but as Carlosdl pointed out, there’s still potential that it’s a cross-platform virus that will attack both OS’s.

I took this from the last paragraph:

“Although there is nothing inherently insecure about running virtual OSes on a desktop machine, they are vulnerable to the same threats as OSes on physical hardware. Therefore, you should follow the same security best practices for VMs as you do for physical machines: Patch virtual OSes, run up-to-date antivirus software and ensure that group policy settings are properly applied.”

As for the Mac being infected, if the malicious program was written to run on Mac OSes and you have set up some kind of disk sharing between the host and the guest, then yes, the Mac could get infected, but if it is written to run on Windows OSes only, then it can’t.

Does virtualization make desktop operating systems less secure? It’s about Windows XP running on top of Windows Vista, but some concerns might be similar.