Any USB device will identify itself on connection to the host computer. It does this by three numbers, the VID, the PID and the SERNO.
VID is a Vendor ID. For the micro:bit this is 0x0d28
PID is a Product ID. For the micro:bit this is 0x0204
SERNO is the serial number - this is a unique number allocated to each micro:bit 'baked in' to the nRF51 app processor.
This information is generated by the DAPLink firmware running on the KL26 interface processor on the back of the micro:bit board.
Here is a trace of a session on a Mac book air, capturing this information (Serial number edited out for anonymity)
> system_profiler SPUSBDataType > before > system_profiler SPUSBDataType > after > davidw$ diff before after 20a21,38 > MBED CMSIS-DAP: > > Product ID: 0x0204 > Vendor ID: 0x0d28 > Version: 10.00 > Serial Number: XXX > Speed: Up to 12 Mb/sec > Manufacturer: MBED > Location ID: 0x14100000 / 5 > Current Available (mA): 500 > Current Required (mA): 500 > Capacity: 8.5 MB (8,454,144 bytes) > Removable Media: Yes > Detachable Drive: Yes > BSD Name: disk2 > Partition Map Type: Unknown > S.M.A.R.T. status: Not Supported
Keywords for search: VID, PID, whitelist, identification, ID