Who creates computer viruses?

Marshall Brain, the writer of "How Computer Viruses Work" suggests that there are at least three reasons why people write computer viruses. Marshall thinks the first reason why people write viruses is analogous to why vandals and arsonists wreak their havoc - for the pure thrill of seeing something destroyed, for example, a destroyed hard drive or computer network [Brain 2000]. The second reason is similar to the first but this reason is for the pure thrill of watching things "blow up". Remember the kid in Chemistry class who was a little bit too fascinated with watching sodium or lithium explode in water? The same fascination can come from creating a virus that spreads quickly - the virus is like a "bomb inside a computer, and the more computers that get infected, the more "fun" the explosion" [Brain 2001]. According to Sophos, most virus writers tend to be male, single, and under the age of 25. Their self-esteem relies on the acceptance from peers or their small electronic community. This leads to Brain's third reason for why virus writers do what they do: bragging rights. If a hole in a corporation's computer network has never been exploited, a virus writer may ask himself, why not exploit that hole before someone else does? I'll show them the hole! You are right it will be more beneficial if they give the time towards the benefit of society.