It's a very different animal.
Sure, MS is better about Windows Security now. And guess what? That's why there aren't nearly as many virus problems as there used to be (think 7's early days vs XP's early days).
Linux has a strong security model. It already has ~50% market share on servers (maybe more)! Don't ever suggest that my last dollar would be spent poorly if I bet on Linux's security.
Also, the plural of "virus" is "viruses", not "virii".
You are confusing whether the system with the users.
The reason why virus is a menace on the windows platform is because of all the non experts using it.
If you had the same kind of types as my partents there would be absolutely no challenge plastering the os with viruses.
That is the MS PR statement, witch is completely BS. Open source have a lot more people looking at the code and using a proven Unix security model.