Everything I download will not open. OS X says the file is damaged and can't be opened and should be moved to the Trash. Like Adobe Reader, for PDF documents. JPEG files will not open. Office files will not open. Yet the thumbnail preview is perfect and I can flip the pages to see the information is there. I tried to download OpenOffice for the Office documents but it says the same thing, damaged, cannot open, should be moved to the Trash.
MacBook Air with Mountain Lion
The problem that you are running into is that Gatekeeper is trying to protect you from malware and not only doesn't recognize the developer "signature" of the App you downloaded it "sees" the file was modified by someone/something other than the developer.
Gatekeeper options are found in Apple menu > System Preferences… > Security & Privacy > General tab (El Capitan shown below) under the header "Allow applications downloaded from:"
Even with Gatekeeper turned off, if you get the "Damaged App" message, you still won't be able to open the file
Per Apple's Support site:
"Damaged" app. – The app has been altered by something other than the developer. This message will appear no matter the Gatekeeper option chosen.
The solution to this is in the info.plist found inside the app. If you set the following key values in info.plist, the App will revert to an "Unsigned App" and allow you to install it.
<key>CFBundleSignature</key>
<string>????</string>
Where is the info.plist file located? It's located in the root folder of your App and will be prefaced with the App Name: {My-App-info.plist}
NOTE: You will need a program like TextWrangler (free) to open .plist files or the Property List Editor available in XCode. (My preference is to go with TextWrangler)
Once you edit that file and save it, you will be able to open it by Control clicking (or right clicking) the App and selecting open.
Gatekeeper is there to protect your Mac from the malware that's ever increasing on the Internet. You should only use this solution with Apps that you fully trust. If you are just randomly downloading software and using this solution to bypass Gatekeeper, you will end up with a compromised system. So, use at your own risk.
I got the same message today as well. This worked for me:
To get around this, temporarily disable Gatekeeper as follows:
- open System Preferences and the 'Security & Privacy' options
- Click the padlock at the bottom if it is locked
- Set 'Allow applications downloaded from:' to 'Anywhere'.
- Keep that open, but go back to your finder window
Open JOSM.app it should work this time ...although you still get:
"JOSM.app" is an application downloaded from the Internet. Are you sure you want to open it? -> Click 'Open'
- Now re-enable gatekeeper back in the settings window. Put it back to the default "Mac App Store and identified developers"
I found that on this site - https://help.openstreetmap.org/questions/21301/josmapp-is-damaged-and-cant-be-opened-you-should-move-it-to-the-trash
This seemed to work for me. Yes, I know that it wasn't a .app file, but that didn't seem to matter.
Note: I found this out after the bounty. I still would like to see a better answer, maybe with a cause.
Solution for this is in another thread here: Gatekeeper preventing from opening files from Finder (launching apps is fine)
Short answer: Check /var/db/gkopaque.bundle to see if the file is valid or damaged. In my case this was a zero byte file. Replacing it with a known good copy completely fixed the issue without having to disable Gatekeeper.
I'm leaving this for future desperate users such as I was :)
I've fixed it easily (after losing hours, including a useless Recovery) using a nice utility called SilentKnight. It identified and fixed on its own a database issue on GateKeeper and XProtect that was causing the error.
[Disclaimer: I'm not affiliated in any way with the website or programmer. Use the software at your own risk!]
