Sorry it took me a while to get back to this. I occasionally go through older posts that I missed and follow up on the ones that deserve an answer.

For actual security, I wouldn't rely on either a MAC address or a drive serial number. Both can be changed, spoofed, or can legitimately change when someone replaces hardware, reformats a drive, uses a docking station, changes network adapters, etc.

Also, the FileSystemObject Drive.SerialNumber property covered in this lesson is the volume serial number, not necessarily the unique physical serial number printed on the hard drive. It can change if the volume is reformatted or recreated.

A MAC address or serial number can be useful as a minor convenience for identifying a machine, perhaps as part of a licensing or activation system, but it shouldn't be the thing protecting sensitive data. If someone is determined enough to bypass it, they can.

For a real Access application, I'd normally use user authentication and permissions instead - Windows/Active Directory or Microsoft 365 accounts where appropriate, plus application-level users and roles if needed. Keep the back-end secured in a location users can't directly access, and let the front-end enforce what each user can do. Hardware IDs are at best one small extra layer, not a lock on the door.