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.
- Disconnect from the internet.
- Open Terminal (Utilities -> Terminal)
- Run:
date -u 0818025919
- Command-Q to quit Terminal
- Run the Installer again
The problem is the certificates in the installer expired some time ago, so the OS can no longer be installed. If you're messing with even older versions, you can try using an older date such as 0818025910