Macintosh with OSX 10.5 is a fine distro, incorporating many of the same Nix-ian tools used by Linux. Built upon a BSD variant, (BSDi, FreeBSD, NetBSD), OSX runs OpenSSH, SAINT, uses sudo, and ettercap, snort, xnu (mac address spoofing) and it also has some real security issues, WAIT, that's not a bug, it's a feature?
A great many trojans are available with many personal and unusual slants on the age old virus themes:
http://www.securemac.com/
Once again we find people attempting to indulge in apples/oranges biased thinking comparing one distro's security to another.
http://pcworld.about.com/news/May232005id120964.htm
But just like with Linux, if you are running a Mac OSX on a shared network, you are begging to be pwned. If you surf without trust based controls for Javascript/Java, and use Mail without low level virus controls, you have the intelligence of a ten year old (before the brain can understand and equate risk and consequences).
Symantec is one of the best tools; but great many exist (use the Source young Jedi).
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