haha sorry to burst your bubble but thats not true at all. Yes macs are much less susceptible to malicious software, due to several things. One being most hackers focus on windows because of its popularity and their hate for bill gates. Also macs web browsing is not built straight into the OS file system. (internet explorer is an extension of the service used to browse the file system). There are several other issues that make macs more resistance but to say its impossible is absolutely false.
Malware is just software that exploits the unsecured areas in the system. So far, no OS is perfect and therefor loopholes can always be found. Virus can even be written for linux systems(although the damage will not be as bad due to the fact that the root user is only used for system management).
So long story short: yes macs are way less likely to get virus, but that definitely doesn't mean its impossible and one day they might have just as big of a problem as windows.
sorry bout the spelling