HotHardware has an editorial about viruses and how they (don't) affect operating systems, you can read it at HotHardware.
There seems to be a recurring phenomenon in the technology press, where any trojan that affects Linux or Macs becomes front page news. On the other hand, trojans that affect Windows are mostly ignored, perhaps because this is considered to be the normal state of affairs.
There are two common statements made in the discussions of these rare events: 1, No operating system will ever be secure from Trojans and 2, Linux/Mac only have fewer viruses because no one uses them. The first statement is almost correct, whereas the second one is a flat out myth in my opinion. Let me explain, and I’ll listen if you still disagree after reading the following in its entirety.