what do I do if the macOS update IS CORRUPTED and won't let me install it
What do I do if macOS High Sierra is damaged, and can not bed used to install macOS
MacBook Pro 15″, OS X 10.10
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If you get a corrupted message...
Naw, not damaged, it's just that you have an old copy already in Applications, there are 2 cures...
Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS High Sierra App in Applications, so expired Certificates are not expired.
Or... trash the Install MacsOS High Sierra.app in Applications, empty trash & restart, then a new copy of a more recent version can be downloaded…
Don't use FireFox or Waterfox for this link…
https://itunes.apple.com/app/macos-high-sierra/id1246284741?mt=12-