If I may make a comment on this…consider this …that any devise that connects with the internet can get infected and unless it has an appropriate protection program on it how can the owner know if it is infected ? I suggest that the first thing you will know of the infection is when you get site redirects or people accusing you of infecting them with emails or it refuses to connect to the internet because that connection has been wiped out by the infection you did not know you have .
I think others above have also said that no machine is immune from infections just because of the OS it happens to have on it .
As far as I am aware it is the Windows OS that is majorly targeted as it is the major OS out there but that is not to say that those who wish to can and will target the other OS’s 