When I first went onto the web, I took advice and used Norton. In a short time I received KakWorm, which did not make itself obvious but changed fonts and things to annoy you. Norton couldn't find it, despite having a seperate code to remove it. I knew I had it because the relative who gave it to me told me so, and finally a pal put me onto InoculateIt, which was free and worked in parallel with Norton. This promply found and removed the worm. InoculateIt is now part of ETrust Easy Armour and is no longer free but is still pretty cheap.

I think no-one will claim a perfect virus-killer, because they work in arrears, reacting to the virus-writer's action.