This is a bit unusual. I think we're going to see more of it, though.
It's a trojan that requires user interaction/permission to install, so a bit of wisdom on your part should be enough to protect you. Should you have less than savvy users, though, something like this might signal the need to run an anti-virus on your Mac. They ARE available and while the OS seems not to require one, the foibles of it's users might.