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If you have attempted to use a MacOS installer application recently, you may discover an error message stating something like “This copy of the Install macOS Mojave.app application is damaged, and can’t be used to install macOS.” This prevents the installer of macOS from working and running, and essentially makes the installer applications useless.
The cause of this error is an expired certificate, and because the certificate is expired the “Install macOS” app for Mojave, Sierra, and High Sierra will not run. Fortunately, there is a fairly simple solution to the “damaged” installer problem.
Resolving “Install MacOS Application is Damaged, Can’t be Used to Install MacOS” Error Messages with Mac OS System Installers
The easiest way to resolve the “This copy of the Install macOS .app application is damaged, and can’t be used to install macOS.” is to re-download the installer again from Apple, which contains a new fresh certificate that is not expired. The links below point to Apple resources where you can find or download the updated macOS installers for Mojave, High Sierra, and Sierra :
- Find macOS Mojave from Apple here – ( direct App Store link )
- Find macOS High Sierra from Apple here – ( App Store link )
- Find macOS Sierra from Apple here – ( direct download link )
You may need to reboot the Mac after you have downloaded the new (and valid certificate) installer application, particularly if you had already launched a version that showed the application damaged error message.
If you do not download new versions of these macOS installer applications, you are likely to encounter the error messages for each release if you attempt to open or use the MacOS installer, or even a USB boot drive created with one of the expired installers:
“This copy of the Install macOS Mojave.app application is damaged, and can’t be used to install macOS.”
“This copy of the Install macOS High Sierra.app application is damaged, and can’t be used to install macOS.”
“This copy of the Install macOS Sierra.app application is damaged, and can’t be used to install macOS.”
If you want to see specifics and the expired certificate itself, you can investigate .pkg components of the MacOS Installer with tools like Suspicious Package and pkgutil, which can show the expired certificate that causes the error message :
Similar issues have happened with various Mac OS installers in the past. Aside from re-downloading the installer, another option that some users have reported to work that gets around these sort of error messages for installers (and sometimes apps too) is setting the Macs clock back in time (in this case, before October 2019 when the certificate expired rendering the installer application unusable), but that apparently doesn’t work all the time with the Install MacOS Mojave app. It’s also not always a practical solution to adjust clocks particularly if you plan on widely deploying, using, and archiving the installer apps for various MacOS releases and on different hardware. Instead, just re-download the new versions of “Install macOS.app” that you require, and keep those around instead.
Many Mac users like to maintain a repository of MacOS installer packages for older versions of system software. For example, I have a collection of MacOS installers including for Mac OS X Snow Leopard, Mac OS X Mavericks, MacOS High Sierra, macOS Sierra, macOS Mojave, and MacOS Catalina. These can be used to build USB boot installers, restore systems, troubleshoot, perform clean installations of the various system software versions, perform upgrades to specific system software releases, and serve many other purposes. If you have a similar installer archive, it’s probably a good time to replace those installers with the new versions that won’t be expired.