AntiVirus - some fundamental questions

[ErikJan]

I have some more basic and fundamental questions about antivirus tools and how they work (not super technical BTW). So I posted on McAfee's own forum. My questions are generic and not related to their product, but I use their tool so I thought posting there was logical.
There was an answer to my first question (I want to slowly build towards the points I wanted clarified, so there's a series of assumptions I'm seeking feedback on), however already at my second question all has remained without response, almost as if no one is watching (or no one knows?).
Anyway, as this is my favorite forum anyway I was wondering if there mighty be some expertise here and/or if someone could point me to a location where I can try again (with a higher chance of success...).

[PaulB]

I am sure there are many Loungers here with expertise in AV ranging from basic to expert. Try your questions here. The worse that can happen is that you will be redirected to a more appropriate site. Other Loungers here may also benefit from the thread.

[ErikJan]

OK, here we go (I didn't say this would be difficult and I think I know most of the answers but I'm seeking confirmation as well).

First question... In general when working on a computer and not browsing the Internet, if I only browse my harddrive / NAS / external devices and do not execute anything infected itself, can I get 'infected' by a virus or malware?

(and if yes, how?)

[StuartR]

You can get infected by a worm if you have a network connection. This could come from another device on your network, or less likely through your router's firewall.

[ErikJan]

OK, let's assume the network itself doesn't add anything here... can I get infected if I browse my home network and PC?

[StuartR]

Yes you can. Because things can lay dormant on your home network waiting for an opportunity to step on to a new computer

[ErikJan]

If my computer has an active antivirus program and all is OK, then if I only browse my harddrive / NAS / external devices and do not execute anything infected itself, can I get 'infected' by a virus or malware?

[StuartR]

It is ALWAYS possible, a determined attacker can attack your router and get through it to your computer. This would require zero day vulnerable that can't be detected by your antivirus software. You are probably safe enough unless a government agency or similar is after you.