[cymbeline]

Doesn’t each processor chip (the CPU hardware) have a unique serial number. Couldn’t that be embedded in various outgoing messages?

I’d say don’t use a computer or phone if you are really concerned about being snooped on. Maybe not mail either. Try to communicate with a wink of the eye.

[Myrddin]

Access to the CPUID in an Intel CPU is selectable from the BIOS. It can be shut off. Another source of keys that are not as easily protected is the TPM module. It is epoxy potted and soldered to the motherboard. The keys inside are employed to encrypt the attached hard disk so that relocating the disk to a different box yields an unreadable drive without the TPM keys.

MAC ids on network and motherboard interfaces are often in EEPROM and capable of override for spoofing purposes. Some vendors use a MAC ID as a license key. That was viable when the manufacturer generated an immutable key for the network interface. That's not the case anymore.

Finding ways to track your activity will be a perpetual cloak and dagger effort. New ones will crop up soon after you've nailed the ones you discovered.