I have decided not to install any anti virus software, even though my son's computer had the trojan. I have decided to just turn off Java and tell my son to be more careful with Adobe updates - you can always install upgrades by running Adobe itself if your not sure of the prompt. I think he most likely became a victim this way (Facebook etc. not really concentrating and installed the fake Adobe Flash upgrade) with the original variant. This was the smart one which erased itself if littlesnitch or (ahem) antivirus software was detected. This is the one which can be removed using Terminal as described, seems to work. As he didn't have any software to detect it I think he had it for awhile, but one of the symptoms he had noticed recently (last week or so) was Safari crashing strangely. Which is what is reported to happen, increasing instability leading to crashes. He's on Snow and I only mention this in case anyone else has seen Safari crash recently, you might be infected.
The new version is it seems both more sneeky and less sophisticated. It gets in via Java and can install without your knowing even if you don't stupidly type your password. However without Java and Flash neither variant could have got in! It installs whether or not you have little snitch (why I say less sophisticated) and that is how it was spotted, little snitch snitched on it.
The other thread has a link to the apple discussion where it was first picked up. If you go to the beginning it is quite interesting to see the apple community slowly wake up to the problem. I'm sure though there wouldn't even be a discussion on a PC site about a windows malware threat, no news there, how many thousand malware threats have been seen on PC's in the same time frame? It says a lot that one trojan for macs has caused so much discussion.
Still I guess if macs continue to grow in popularity there will inevitably be a time when we lose our peace of mind and have to install anti-virus. Not yet though, but watch this space!