Why is there almost an endless number of malware for windows, and hardly any for mac. Is it because Mac has less holes? NO! It has nothing to do with this (I will moderate this statement later). The reason is that 95% (more or less) of users are running windows, and the rest is all other systems. What has this to do with it you ask? Try looking at it from Joe Hackers perspective. He wants to get lots of zombie computers to send spam to make money (this is a typical Hacker of 2006, hackers aren't what they used to be). The question he then asks himself is something like: "How can I get most zombies for the least amount of work? Lets see. If I make a website attacking all the visitors running safari on osx i'll get about 10-20, if I on the other hand attack IE on Windows I'll get 1-2 thousand. In other words: using 1 hour to attack safari on osx gives me a little money. Attacking ie on windows gives me MUCH money" I wonder what he chooses to do?
Security is chiefly NOT a technical issue, its a human issue, as it is humans that initiate security-attacks.
On the other hand, if it, technicaly, is a thousand times easier to attack mac than a windows, then it will be worth while to atack macs to.
The biggest reason we have so much spam in our mailboxes is windows and its marketshare, and its userfriendlyness.
I've stopped helping friends with windows that dont run an antivirusprogram. This I tell them is the hidden cost of running windows, and it has nothing to do with windows being technically inferior to mac securitywise, its purely numbers.