Steve,I have an open TAC case about this 'security' problem. Please open one also and ask to attach your case to BugID CSCdz02697 and CSCdt48779.Thanks,Matthijs
If you are using CM 3.1 with MOH it is most likely a codec problem.Service>Service Parameters>"YourServer">Cisco IP Voice Media Streaming App>DefaultMOHCodecMake sure you either select all the codecs or specifically the one you are using.Take it easy...