This Trojan is one of the most advanced Trojans they've ever seen. It doesn't "show" itself and doesn't do anything to your computer to where you can tell something is wrong or it's infected; it just runs silently in the background, stealing your banking information, passwords, log-ins, address books, etc. Because of how advanced it is, it's been able to be "dispensed" for over 3 years by the same people - to both PC's and Macs.
You're right, usually viruses were aimed at Windows users and didn't affect Macs as much - but that was because not as many people used to use Macs as they do now. With the growing popularity of Apple more and more people are using Macs so viruses and Trojans are being written to infect them as well as PC's.
Here is a link that has different information on anti-virus software that is for Macs:
It includes some reviews of the more common Antivirus software, like MacAfee and Norton, that are made for Macs. I don't personally use a Mac so I can't really give a whole lot of advice as far as which one is better versus another.
For my antivirus software for my PC I use Antivir. It's free and I haven't ever had a problem and I've been using it for about 6 years or so. The only thing is that with this particular Trojan, even though some Antivirus programs are catching it and deleting it or quarantining it, it has the ability to reinstall itself because it has a rootkit written into (technical term for it can't be deleted without a special program that specifically looks for that rootkit). That's why it's recommended to use something that is specifically written to get rid of the Trojan.
If anyone is interested, http://www.free-av.com/
is where I get my antivirus. Just click on download and then click on the one on the left - Avira AntiVir Personal.