https://itresearch.en.ecplaza.net/
If I bought the system, I bought the code.
Functional expressions are not copyrightable. If I own a copy of the code you wrote, I am reasonably allowed to extract those purely functional expressions into my own work. Purely creative expressions are still protected by copyright. (This is why you cannot copyright an encryption key.)
When no “owner” exists, the licensing agreement is no longer valid. Copyright is a different issue. See above.
If the code is covered by patents, extracting it doesn't give you anything that reading the public patent wouldn't (if the patent was written as it should have been, to inform, and not obfuscated or ran through incomprehensible legal jargon).
And if it's a trade secret, then you relinquished it the moment you sold objects containing it. Though I realize DRM/anti-reverse engineering laws are trying to take away our right to examine how stuff works, they are absurdly immoral laws, and breaking them should never be described as "theft".
Whether you're talking about a $0.30 MCU with the lock e-fuse programmed, or a several-hundred-dollar (or more) SoC with triple-redundant power-management/security cores booting using unit-unique payload decryption keys burned into security fuses, the adversary might be able to get what you're trying to protect.
How paranoid you want to be about readout protection will vary depending on your goals. If you want to do a decent job blocking reverse engineering of a product to impeded clones being produced, the lock bit might do the trick.
