The PhysicalAddress property returns the Media Access
Control (MAC) address for an Ethernet or Token Ring network adapter
installed and configured on the local system. Since it is
guaranteed that every adapter is assigned a unique address
throughout the world, this value can be safely used for
identification purposes. It is possible that this property will
return an empty string, which indicates that it could not find a
network adapter.
If more than one physical network adapter is installed on the
system, this property will return the MAC address of the first
adapter that it finds.