The way Mac fans always claimed immunity from has virii always annoyed me.
In the early 90s there was an outbreak of a cross-platform MSWord macro virus which kept repeatedly flaring up where I worked. The PCs were not networked in our department - so the virus was being spread via floppy disk. After one frustrating flare-up, I was able to trace the movement of some floppies - and realised the source of the reinfection was an Apple Mac! We only had one mac, which one of the secretaries used for DTP (on Quark) - but she also ran MSWord and would import & tweak documents. Every floppy that touched that mac came back infected - but as the received wisdom was that macs were immune, nobody had thought of checking the machine.