Viruses affect the OS, not the chip. Until Mac becomes a less robust system, it will continue to have the virus immunity afforded by the OS.

When a popup shows up on your screen telling you that you have a virus, more often than not it is a popup ad from the browser, not an actual virus.

system security advice? Turn OFF windows messenger. As a default it is on, but leaving it on opens up a direct path to the OS. To turn it off, go to the start taskbar, settings, control panel, admin tools, then double click on services. Find messenger in the task list, double click on it, and disable it. This will not affect the computer, unless you are on an administered LAN, in which case check with your admin people.

Set up your virus scan to scan all downloaded files on download. This varies between a/v services.

AVG is excellent a/v protection, you most likely have autoscan on d/l turned off, which opens a hole for a virus to get in.

I would also reccomend downloading the free lavasoft ad aware s/w, and spybot S+D. these will give additional protection, as there are viruses which get into your system through adware.