low tech option to a hi tech problem (Score 1)

Seems to me that attempting to locate 1 network device on a network of that size would be a pretty difficult task. Kind of like trying to find a needle in a hay stack. I would that one that could be done is temporarily decrease the size of that network to only the pc's and devices that are absolutly needed. In other words manually power off the unneeded devices & PC's. That should make the haystack a bit smaller. If all of sudden the black box goes silent then the device might be a virtual machine. Bring up the devices one by one until you find your black box. This guy probably put some thought in to it and would expect the device to looked for using tools like tracert, etc..