This functionality is not available in LabVIEW RT. If you attempt to switch execution target to an RT controller already targetted by someone else, it will tell you too many hosts are connected and fail. Of course if it allows you to switch, then no one was connected. By attempting to switch execution target you can use the message above to determine if anyone is targetted or not, but if someone is, there is no way to determine who.
If you are concerned about this sort of thing, you might check the RT target options in LabVIEW RT to change the IP access list for hosts that are allowed to switch execution target to it.
