The game Secondlife has been struck by a virus according to this article. It manifested itself by glowy rings in the virual world, which multiplied everytime somebody touched them. By human nature these rings were touched by people and started to multiply exponentially leading to heavy database loads. Therefore Linden Labs (the company behind sencondlife) had to shut down access to the world to "clean" up the virus mess.

Are vitual worlds better because they can be shut down? Imagine how easy it would be to clean up the polution in the world!