Rule--Sid12172--Summary:This event is generated when an attempt is made to send a malformed communication to a Voice over Internet Protocol (VoIP) device.--Impact:Unknown.--Detailed Information:This event indicates that "Inbound 501 Not Implemented Message" has occurred.Some events may indicate that a VoIP device is in use on the protected network. This may be a policy violation.--Affected Systems:Devices using VoIP.--Attack Scenarios:This is a possible policy violation, it may be that a VoIP application has been installated on a client host.--Ease of Attack:Simple.--False Positives:None known.--False Negatives:None known.--Corrective Action:Check the device for signs of compromise.--Contributors:Sourcefire Vulnerability Research Team--Additional References:--