reating a macOS installer on a bootable USB drive provides a convenient way of installing a fresh copy of macOS on multiple Macs, and also allows you to perform a clean installation quickly and easily.
If you tried to run your installer recently and unexpectedly received an error that it is damaged and can’t be used, then don’t worry – keep reading for a simple and straightforward way to fix it.
Why is my macOS Installer Damaged?
If you tried to use a macOS installer in the last few days or weeks, you may have been met with an error message saying something like “This copy of the Install macOS Mojave.app application is damaged, and can’t be used to install macOS.”
As Apple explains in a newly published support document, the likely reason for the “damaged” error message is an expired certificate. Happily though, the fix is very simple.
Read more at MacRumors.com