Once a device is discovered, the only way to delete it is to disconnect it from the network (see "Deleting a Device"). If the device is plugged back in, it will be re-discovered. 

To disable automatic device discovery

1.Open Main Menu > System Administration (Ctrl+Alt+A) > General tab

2.Uncheck Enable devices and servers auto discovery in the System Settings section

3.When finished, press OK to apply or Cancel to discard changes 

 IMPORTANT:  Once auto-discovery is disabled, new devices and servers will no longer be auto-discovered, they will have to be added manually.