It really only makes sense for nodes with the port forwarded to remain on the IRC channel, right? Maybe it could just ping a php script or another node randomly (this might be a better idea) which tells it YES/NO on whether the connect-back is working, and then just terminate the IRC thread if it’s not needed anymore. It could re-probe every 6 hours or so in case the user changes their port forwarding settings, or it could just be an option even..
Re: Security
Figures: Laszlo Hanyecz