I maybe getting myself into hot water here, but I have observed that any of the pcs/laptops that have come into the shop with virus’s on them nearly all have the same reason for the infections in common and that is,
they have free antivirus software installed
or no antivirus
or the antivirus they bought before has run out
but mainly it had free antivirus software installed. The analogy I use here is that free antivirus is like a house with the door locked and the windows open!
So I recommend to people to buy really good antivirus software. At www.computerfix.ie we recommend and sell Bullguard Internet Security.