I believe it's a virus, a bit like MS Blast, in that it works by infecting vulnerable PC's connected to the internet (rather than by email).
If your firewall is detecting it I assume it is also denying access too. It's a good idea to make sure your patches are up to date just to be sure though.
If you are patched then you are safe (I think) as it uses the same vulnerability that MSBlast did, which MS issues an urgent patch for a little while ago.
Given that your firewall software is also picking it up, I wouldn't worry too much.