Re: Shooting themselves in the foot? - yes, by releasing Win 8.
There are 'Linux' viruses, there are 'Linux' worms, there are definitely 'Linux' rootkits and malware. Sure, many of them require retooling due to the heavy fragmentation of the ecosystem, and they are often closed relatively quickly compared to how things work in the land of Redmond, but they exist. It is a highly targeted system because of its big iron presence, where have you been for the last decade?