Last post this year!
History: I suspect No2 son had visited a few torrent downloads and the like - I have beaten him with a large stick
AV-wise, as Tarq says - none are perfect. No2 lad was running AVG, but I have no idea what settings or update state so I would not place any blame. Virut is a particularly 'nasty' one and like many others disables AV as a first step.
I do believe in having a 'cocktail' of progs to run at intervals. I use Avast, but it lets some through, as does AVG and Avira - none are perfect. I run Norman 2009 and MBAM at fairly frequent intervals. There is also Housecall from Trend, and Panda which have promise. 'Nasty' viruses are rapidly becoming a fact of life - best defence is a non-admin profile, but that can be a pain in itself. As Tarq says - if you 'click it in', there is little you can do to stop the really bad ones. The 'traditional' viri will be stopped by AVG and the like, but the determined ones will get through if invited.