Report for Unknown Devices.
On the Manage Monitored Devices Screen, Use the filters at the top and set up this criteria:
Device Type IN Unknown
Then hit the Report button at the bottom of that screen.
That will give you a report-style list of all of your unknown devices.
I hope that helps!
You can modify the report 'Count of Messages by Device' which is in the Adhoc---Network---System---Statistics folder and add to the where clause AND category1 IN ('unknown')
Does that work for you?