first known polymorphic metamorphic virus for win

According to Symantec it can.  Any computer can be infected with some kind of virus or another I believe.  Linux just hasn't been hit because a linux virus will infect about 3% as many people or less as a standard Windows virus.  People writing viruses want a large impact so normally they'll go for the larger user base (windows).  When Linux is more popular you'll see more viruses for it.