First let me say that I'm a long-time Linux user - the first time I installed it was in 1992 from a giant stack of 3.5" floppies. While Linux is extremely secure and can be locked down via various methods, you still cannot say that it is immune to virus infections. If the system is poorly designed and managed, is not using proper protection for services (AppArmor, chroot's, etc) then it can still be vulnerable.
Linux's primary advantage still remains that it has a smaller install base and is therefore a smaller target.
I'm not sure that Linux would be much more secure than
Windows if it was in as wide usage - the largest factor in computer security will always be humans.
Look how easily the recent Flashback virus spread on Mac's - people will continue to input their password when prompted.
It's not really "extremely" secure. Look around, you'll find that at any given time there are probably a couple local escalation exploits, at the very least.
Linux's primary advantage still remains that it has a smaller install base and is therefore a smaller target.
I'm not sure that Linux would be much more secure than Windows if it was in as wide usage - the largest factor in computer security will always be humans.
Look how easily the recent Flashback virus spread on Mac's - people will continue to input their password when prompted.