As I wrote on the Internet Storm Center:
First reported by Intego, this trojan apparently is distributed by downloading Bittorrented copies of iWork 2009 from the Internet and installing them. The Trojan is installed as part of the software package, by, yup, you guessed it, you giving the software permissions to install by giving it your password.
Apparently this backdoor opens a hole on your computer, reporting back to a central server in order to allow the attacker to connect and issue commands to your system.
So, what can we learn from this?
1) If you Bittorrent software you are supposed to buy, and break the law in doing so... you have to deal with the ramifications...
2) Hey, you can download the Trial from Apple.com, and then buy it, and they give you a serial number! You don't even have to go to the store to get a boxed copy! You already spent the money and bought a mac, you cheepskate, now if you want iWork, spend the 79 bucks and buy it like you are supposed to.