Certain applications downloaded from the Mac App Store gave problems this week, with users reporting that the apps would crash and display an error message.
“[This app] is damaged and can’t be opened. Delete [this app] and download it again from the App Store,” the alert said.
He showed that the security certificate issued when downloading an app from the Mac App Store had expired at 21:58 GMT on 11 November 2015.
Apple has reportedly created a new certificate for App Store apps which will expire in April 2035.
Users have reported being able to get broken apps working again by disconnecting from and reconnecting to the Mac App Store, while others have had to uninstall and reinstall affected applications.
Some have reported that a reboot fixes the problem.