Although it is common knowledge to most people (well actually not most as it turns out) antivirus solutions on home users windows installations should be provided by free software.
The most obvious solution is to install firefox instead of the old dog internet explorer 6 which will stop a lot of the attacks from actually happening in the first place.
Then I would personally recommend that you take a look at Avast home user for your virus protection as it has the facility to do a complete boot time scan which seems to find virus that others (AVG!!) do not.
But softpedia has comiled a list of all of some of the free anti virus software around today and unsurprising they come to no real solutions or preference. Is this because all three players reviewed also put some money into softpedias advertising fund or am I just being a bitch?
Windows