I didn't mean that linux or Unix would become a payed for software, I don't think it ever would happen to be honest. I meant that linux and Unix will become more popular in the future, at least i hope. They still have a while to go, Gaming is one of their serious down-falls in the eyes of an consumer, I have a linux box over here, but would never consider switching exclusively to it because I don't want to deal with half working emulators like Wine.
But on the area of hackers and malware, I think otherwise. Hackers aren't attacking Windows or M$, they're attacker users, people whom they don't know, and aren't familiar with. When someone puts a self-replicating virus on the net, they don't care where it ends up, they're just getting off on their abilities. And where else to do this than the billion-user wide Windows system? More people to screw with. If linux or Unix became more popular it would have some of the same malware problems windows has, but not all by any means, because both these open-source operating systems are inherently safer.