The FTDI-chip provides a unique serial-number.
There is a manufacturers name and number and it is possible to change this.
Just for clarification:
Every USB-device has a vendor-ID (something like the “manufacturers name”) and a product-ID. The product-ID stays the same for each “type” of chip.
For instance every FTDI USB2Serial-converter on the Arduino has a vendor-ID of 0x0403 and a product-ID of 0x6001.
It is not a good idea to change any of these numbers because the standard drivers for the device will stop working and have to be patched to recognize the arduino-board again.
Then there is the serial-number. This is a unique number (or better a combination of numbers and characters “FB675TZ6”) burned into each chip, so there should be no reason to change it.
On Linux you can do some very cool stuff with these numbers. My Arduino that drives a LedMatrix for instance appears at a port named /dev/LedControl another one that runs the bitlash-shell at
/dev/bitlash. I don’t if Windows provides similar functions.