Me too, but from what little I understand when they write a virus for Windows they only need to write it for a specific version, like XP or Win7. But to write a virus to infect Linux systems would need to be written for whatever varients you want to infect, and there are many, plus the virus would need to get past the Linux feature of having to supply the root password to modify the OS. It's easier to write a virus for Windows, you have more potential targets and most Windows users are pretty clueless when it comes to security. Also, I would bet "professional courtesy" in the virus writer world makes it "bad form" to infect Linux systems since it might infect other virus writers.