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Message: <blockquote data-quote="MacInWin" data-source="post: 1909362" data-attributes="member: 396914">If it is running Monterey, the installation process creates a hash code for the files as they are installed, then creates from the hashes a "master" hash that is then compared with what Apple thinks the hash should be. If they match, then the installation is a success and the files are as expected. Each boot the hash of the boot system is again calculated and compared to the hash of the installation. If they match, that's fine. If they don't, you get that message to say that some file in the installation no longer matches what was installed and you should reinstall the OS again from a known good installer from Apple. Basically, it is a security check at boot that ensures what you boot is what Apple installed. As was told, backup your data drive and reinstall the OS to correct the situation.</blockquote>