Surely not the viruses and spyware. All of them?
Using Boot Camp boots the Mac into a full fledged WindowsXP Pro OS... and it would be just as susceptible to ALL of them as a Windows XP on any other maker's box. They couldn't touch the Mac OS X partition though.
I run AVG, MS Anti-Spyware, and Spybot Search and Destroy on my Windows XP Pro installation on my Virtual PC... and I DON'T surf the web or receive email on it... except to upgrade the anti-ware and their definitions.
Good nite, JS