Anyone who thinks Macs are immune from this sort of thing is under a serious delusion.

Less attractive to malware writers because of lower market share: yes. (As their market share grows, which it seems to be doing, they may become more attractive this way, but for the foreseeable future we're still talking single-digit percentages.)

Harder to crack because of the Unix underpinning of the OS: yes.

Immune: no. This just proves it.