Currently, the media in most contries is full with stories about how this man "trained" with computer games. Here in Denmark - which is my country -, we too have had our quantity of stories about this and including long evening broadcasts on tv about this man and his training with computer games.
I believe, that some patterns of thought can be trained by playing computer games and including the "violent" computer games. I also believe, that children, who have no upbringing by their parents and have no standards of normality set by their parents or other adults, can be affected by anything - including, but most certainly not limited to, media like computer games, movies, tv, musik and media in general.
If you have had any upbringing as a child, then you can be affected by anything. For those of us, who are more normal or at least have had an upbringing, computer games continue to be a fantasy world. I do not belong to the group of people who want to believe that computer games begets violence at all - on the contrary, as some of the more sane psychologists of our society argue.
I think it is much more interesting to focus upon from where the man got his actual weapons, his ammonition and his bomb making materials. Norway is not exactly like e.g. the US, where every madman end every grandma can get anything in terms of hand guns and where people drive around with 25 weapons in the trunk of their cars and shoot at will. Hopefully, the current court trial in Norway is going to focus less on the computer games and their fantasy worlds and more on the actual actions and the origins of the applied remedies.
As a normal person, I too love computer games - first person shooters in particular, since I think that the WoW kind of games are most lame or that they at least have no appeal to me at all - and within these virtual worlds I too love to "kill" teenagers one third of my own age and just for the fun of it.
I hope the world never again sees doings like what happened in Norway; it is a tragedy.
The usual chitchat about violence in the real world and the virtual worlds of computer games has been going on for at least two decades and will never see an end, sadly.