Why the “.app is damaged and can’t be opened” message appears

macOS’s Gatekeeper adds a quarantine attribute to files that are downloaded from the Internet.
If the app’s code signature can’t be verified (or the attribute isn’t cleared), Gatekeeper shows the “damaged” alert even when the bundle is perfectly fine.
In other cases the download really is corrupted or the app isn’t compatible with your hardware (e.g., an Intel‑only binary on Apple Silicon) — both situations trigger the same dialog.

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Step‑by‑step fixes

#	What to do	How / Command	When to use it
1	Restart your Mac	–	Clears transient Gatekeeper caches; often enough for a one‑off glitch. 1
2	Delete the current copy and reinstall	1. Drag the app to the Trash → Empty Trash 2. Re‑download from the official source (App Store, developer site) 3. Install again	Works when the original bundle was corrupted during download or transfer. 1
3	Open the app via the context menu	1. Control‑click (or right‑click) the app in Finder 2. Choose Open 3. Click Open again in the warning dialog	Bypasses Gatekeeper for this launch only. 8
4	Remove the quarantine attribute	sudo xattr -rd com.apple.quarantine /Applications/YourApp.app (replace the path as needed)	Needed when the app is from the Internet and Gatekeeper is blocking it. 35
5	Temporarily lower Gatekeeper’s strictness	sudo spctl --master-disable After the app opens, re‑enable with sudo spctl --master-enable	Use only if the above methods fail and you trust the source. 5
6	Check for macOS‑compatible version	Verify the app supports your architecture (Intel vs. Apple Silicon). Look for an “ARM64” or “Universal” build.	Relevant for Apple Silicon Macs where an Intel‑only binary will be rejected. 7
7	Update macOS	System Settings → Software Update	New releases add support for newer signing algorithms and binaries. 2
8	Contact the developer or Apple Support	Provide the exact error text and macOS version.	If the app’s signature is truly broken or the issue appears with many apps. 14

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Detailed instructions

1. Restart your Mac

A quick reboot often clears temporary Gatekeeper state and lets you try opening the app again.

2. Delete & reinstall

1. Open Finder, locate the problematic .app and move it to the Trash.
2. Empty the Trash.
3. Download a fresh copy from the App Store or the developer’s official website.
4. Install and launch the new copy.

3. Override security via Finder

1. Control‑click (or right‑click) the app icon.
2. Choose Open from the shortcut menu.
3. When the warning appears, click Open again.
   This adds an exception for that specific bundle.

4. Remove quarantine flag with Terminal

1. Open Terminal (Applications > Utilities).

2. Run:

   sudo xattr -rd com.apple.quarantine /Applications/YourApp.app
   

3. Enter your admin password when prompted.
   The -r flag removes the attribute recursively from the bundle’s contents.

5. Adjust Gatekeeper (use with caution)

sudo spctl --master-disable   # enables “Anywhere” option
# After the app works:
sudo spctl --master-enable    # restores default protection

6. Verify architecture compatibility

• On Apple Silicon (M1/M2) Macs, ensure the app is Universal or ARM64.
• If only an Intel binary exists, run it under Rosetta 2 or look for an updated version.

7. Keep macOS up to date

System updates often include newer code‑signing requirements and compatibility fixes that can resolve the error.

8. When all else fails…

• Reach out to the app developer for a signed, up‑to‑date installer.
• Contact Apple Support if the problem appears with multiple unrelated apps, indicating a possible system‑wide issue.

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Quick checklist

• ☐ Restart Mac
• ☐ Delete & reinstall the app
• ☐ Try Control‑click → Open
• ☐ Run sudo xattr -rd com.apple.quarantine …
• ☐ (If needed) Temporarily disable Gatekeeper with spctl
• ☐ Verify app matches your Mac’s CPU architecture
• ☐ Install any macOS updates
• ☐ Contact developer or Apple Support

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Tip: Always download software from trusted sources. If you must bypass Gatekeeper, do it only for apps you’re certain are safe.

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