Thanks for the reply! It didn't find either mIRC itself or an mIRC script (didn't have one installed at time of scan). When it was scanning memory and system files, it would find malware.bkdr_ircflood.x if mIRC was running. If mIRC wasn't running at the time, it wouldn't find it.
I'm also scanning using tools from the thread you link right now. Of the few that have completed, only HouseCall house found this virus. I'm beginning to think that it is indeed a false positive detected by HouseCall.