So it's not a virus.
But you're missing the point! Macs are no longer immune! (Oh, happy day!) ;^>
No, it definately requires permission to install and run for the first time. It is a trojan.
According to what I've read, it does attempt to infect existing apps (The last four you ran) but it only causes them not to execute. It has code that attempts to spread copies of itself through iChat... but that doesn't work either.
To get infected one has to actually download, uncompress the file, and then give a JPEG file permission to run as an application for the first time. Unlikely.