A growing number of Mac users are reporting an issue with some apps downloaded from the Mac App Store. The apps display a “damaged” error when they are opened. Most users report the issue popped up on Wednesday.
… The issue appears to be rather widespread, affecting popular apps such as 1Password, Acorn, Byword, Call of Duty 2, DaisyDisk and Tweetbot.
As seen in the screenshot above, (via Twitter), users see the following error message when opening apps downloaded from the Mac App Store:
“App Name” is damaged and can’t be opened. Delete “App Name” and download it again from the App Store.
Tweetbot developer Paul Haddad posted a tweet that says the issue appears to be caused by expired receipts for authentication certification, and mentioned the possibility that the receipts now using SHA256 encryption could be causing problems under older versions of OS X. However, some El Capitan users are also reporting the issues, leading Haddad to pontificate that perhaps apps contacting Apple’s servers at the same time might be causing a “self inflicted DDOS on Apple’s receipt generation service.”
Some users report success rebooting their OS X 10.10 or later machine, while others report they fixed it by reinstalling apps for the Mac App Store, disconnecting and reconnecting to the store, or logging out and logging back in again.
Apple has not commented on the issue as yet.