By the way, here's a real-world example that will question anyone who says you don't need anti-virus as long as you stay away from the dark corners of the internet:
I was searching for various sites about some topic a couple weeks ago. Just something about weather or crime statistics or something. Clicked on what seemed like a news/information site. It seemed to open fine for a moment, then my browser started stalling out or otherwise acting weird. In that quick moment, I knew something bad was up with that website, and in that same moment, Kaspersky popped up and warned me about a virus that was now in my browser cache file. And it probably asked me to block the site. I forget.