Ignorance is bliss, unfortunately on the Internet; it can mean certain abuse. Until I found Steve Gibson's site, I had no clue what was happening (or could happen) while I was surfing the Net.
Try Steve's Tests and see what some people with the know-how, can find out about you while you're happily surfing the Net.
Finding out the worse from his site's tests, I was persuaded to download and install which was recommended by Steve.
That was back in 1998, and now, if my is not on I will NEVER get on the Internet. That's cause over the years I have read all the alerts reports and the MANY attempts to 'scan' and 'probe' my computer using so many different methods.
I know there is nothing to fear as I hold no TOP SECRET government document or I don't run a drug ring from Timbuktoo but I'd get upset not knowing who was doing what with my computer (or worse still, THROUGH my computer - read the excerpt from an article on Steve's site).
The above (very interesting) article on Steve's site describes how a 13 year old kid over many days, staged DDoS attacks on GRC.COM using other peoples' computers!