This is absolutely not true. Such a statement is ridiculous, and ignores the historical development of Linux and Windows. Windows was built as a single-user, administrator-by-default system that will run any EXE file without question. Linux was built modelled on UNIX standards: run as unprivileged user, multi-user environments, etc.
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".