Wow ... the number of viruses is because of popularity, not what can and cannot be hacked. Hacking is not dependent on viruses at all. Have you tried to hack Linux (if you happen to know how to hack)? The OS on the other side only matters because of the amount and type of security. Again I recommend, until you actually use it extensively, you really shouldn't make such assumptions. The reason Linux/Unix is almost unhackable is because of the directory system, which hackers need to get through in order to find the information. Unless there is a program installed in the system that bypasses the normal operating structure of the directories (ie a back door) you cannot get into certain directories without a password, you can even seclude directories from the super user password and make them accessible only with a unique password. Windoze has that option but does not use it, while Linux not only uses it but it's integrated into the system. As for viruses, you have to install them yourself, so as long as you stick with trusted sources, you won't get one, period. Everything that is being installed on Linux has to be given permission to access the system directories or they simply cannot infect your system, even if they are saved in a temporary location, all you have to do is reboot in safe mode and delete them at worst, but rarely even that is required.
I can go on and on explaining this, because I am horrible at explaining it to people who have never used something, but again, until you have used them all extensively or written code for them, you just don't know. I have tried to write viruses for Linux, simply to test security, it's a bitch and a half, but for Windoze I can write them very easily. Even the ones I can write for Linux they still have to piggy back on another program, which the user has to allow it to be installed.