When I got my laptop (a couple years back) I had norton on it but it turned out that it wasn't set to autoscan and it was a couple weeks before I actually ran a scan on it. I found about 72 viruses! i couldn't see where on earth i might have gone to pick up all that... didn't do anything out of the usual...

norton managed to deal to all but one of them. my office mate was a bit of a comp. whizz and so he did as mystry suggested and typed it into google to see what he could find out about it. he managed to find instructions for getting rid of it. he followed the instructions. it did deal to it - but it also took him half a day to get it off my computer.

i currently use AVG virus scanner. it was free to download and it seems to fetch updates off the net (to deal to new viruses) every day. i run it automatically on start-up every day. it does slow down my system considerably (system is getting old now) but i haven't found any viruses (or had any problems) since then. i've heard that no one virus checker is able to find all viruses. some people thus have two different virus checkers. i'm not sure what is reasonable caution vs paranoia, though. i do lots of google scholar searches and visit a few message boards and check email but that is about it really.

i've used hijack this at times, too. i'm a little scared because i'm not sure what some of the stuff is... i'm similarly scared about changing 'auto start on start-up' settings because i'm not sure what some of the stuff is... i think you can type the stuff into google, though, and see. and of course if you get your system to save itself (create a restore point) before mucking around with it you can always restore it to the save point.