Gordon change your browser to Firefox...it seems to be much safer that IE.
My bullguard runs a daily quickscan and a big scan once a week......the quickscan used to pick up 14-20 viruses daily while I was using IE....but now nothing since I changed to Firefox. I am a new convert but I like it.
As for Norton...rubbish and does definitely slow down the machine....didn't like Macafee either......got a trojan while I was running the Free antivirus....so I now have bullguard.
It is cheaper than getting a trojan or a worm removed from your system.......and you can try it free for 60 days.
Free Anti Virus Trial and Internet Security Software - BullGuard.com
Here is a link for you to have a look at.