Regarding VBS and VB Viruses

Ok, first of all please don't mistaken my intention for this thread.

I've been using VB for only about 4 months. I'm interested to know why are VBS/VB virus are so threatening to the system? I mean normally won't a user be notified if a macro or program or something is attempting to run?

And if possible, can someone show me a very simple example cos I'm really interested to know more on this but I'm NOT keen on creating a virus. Just for my further knowledge.

Thanks for any replies!!

P.S: Pardon if my English is not that good.