Some cable user's machine running default-configured MS apps is sending Paul dynamic DNS queries that it shouldn't, because somehow it's decided he's got an interesting destination (I'm guessing f.root-servers.net ?) Paul wants the user to get an error popup about it. Well, default-configured Microsoft applications have an application that lets you send a machine popup dialog boxes; it's been discussed here recently because spammers abuse it and (related discussion) it uses Port 135, so it might or might not be blocked by Comcast.net. So the obvious thing to do is find whichever program it is you use to send those messages, and start sending popups, guessing that it might not be blocked. The user's unlikely to have a clue what to do about them, but if you include a URL, you may get their attention.