“App Can't Be Opened”
Gatekeeper, Explained Calmly

Your Mac Has a Doorman, and He Doesn't Explain Himself Well

Apple builds a security check into macOS called Gatekeeper. Apple's own description is plain enough: it's designed to help ensure that only trusted software runs on your Mac. Before a new program runs, it checks three things — whether the app is signed by a developer Apple has identified, whether it's been sent to Apple and scanned for known malicious software (Apple calls that notarization), and whether anything has altered it on the way to you. Apple also asks your approval the first time you open downloaded software, specifically so nobody can trick you into running a program when you thought you were opening a harmless file.

So the warning is a speed bump on purpose, placed at the one moment when a mistake is expensive. What it can't tell you is the thing you actually want to know — is this app safe, or not? Nothing on that screen can answer that. But the path the file took to reach you answers it almost completely, and you already know that path. That's what the rest of this page is about: what each message means, how to let a good app through in about a minute, and how to tell the difference before you're staring at a gray box.

Which Message Are You Seeing?

• “…is an app downloaded from the Internet. Are you sure you want to open it?” — All clear. This app is signed and checked; your Mac just wants a first-time confirmation. Read the app's name, then click Open. You won't be asked again.
• “Apple could not verify [app] is free of malware that may harm your Mac” — Apple never checked this one. This is the serious one, and it's your call. Run the source test below first.
• “…can't be opened because it is from an unidentified developer” — Same situation: no registered developer stands behind it.
• “…was not downloaded from the App Store” — Your security setting is on App Store only. See the settings section below.
• “[App] will damage your computer” — Not a formality. macOS recognizes known malware, or a signature Apple revoked. Move it to the Trash and don't go hunting for a workaround.
• “[App] is damaged and can't be opened” — Modified, corrupted, or an interrupted download. Delete it and download again from the maker's own site, typed in by hand. If it happens twice, walk away.
• Nothing at all — the icon bounces once and quits. Often the same block, arriving quietly.

Two Buttons That Trip People Up

Move to Trash is usually the highlighted button. That's Apple nudging you toward the safe choice, and nine times out of ten it's the right one. Done simply closes the box — it does not approve anything and it does not delete anything. If you're unsure, click Done and think it over. Nothing bad happens while you think, and there is no timer on a download.

The Only Test That Matters: Where Did It Come From?

1. Did I go looking for this, or did it find me? If a pop-up, an ad, an email link, or a phone call led you here — stop. That one answer settles it.
2. Did I type the maker's address myself? Typing zoom.us or brother.com into the address bar beats clicking any search result — the top results are often paid ads pretending to be the real thing.
3. Can I name the company and find it twice? A real maker has a website, a support page, and other people writing about it. A name you can't find outside the download page is a name to skip.
4. Is there an App Store version instead? Check before overriding anything. Half the time there is, and the whole problem evaporates.
5. Is anyone waiting on me? If someone is on the phone, on a screen-share, or telling you it's urgent — that is the scam, not the app. Hang up and lose nothing.

How to Click “Open Anyway” — the Current Steps

1. Try to open the app first. Double-click it and let the warning appear. Nothing shows up in Settings until you've done this.
2. Click Done on the warning — not Move to Trash, if you're keeping it.
3. Apple menu > System Settings > Privacy & Security.
4. Scroll down to the Security section. You'll see a line naming your app — something like “was blocked to protect your Mac.”
5. Click Open Anyway, and enter your Mac password or use Touch ID if asked.
6. The warning reappears once more. If you're still sure, click Open. The app is saved as an exception and opens normally from then on.
7. Button missing? Apple's Mac User Guide says Open Anyway is available for about an hour after you try to open the app. Double-click the app again to restart the clock.

The Right-Click Trick Doesn't Work Anymore

For years the standard advice was: right-click the app, choose Open, click Open again. Half the internet still says so. Apple announced to developers in August 2024, ahead of macOS Sequoia, that users would no longer be able to Control-click to override Gatekeeper for software that isn't signed correctly or notarized — they'd need to visit System Settings > Privacy & Security instead. That's still how it works today. Apple also closed the old Terminal command that turned Gatekeeper off. Why? Because the right-click trick was easy to talk someone through over the phone — two clicks, no password, no reading. Moving the override behind a scroll, a password, and a second confirmation costs an honest person forty seconds and costs a scammer their entire script. And a word on the Terminal commands you'll find in search results: what they actually do is strip off the tag marking a file as downloaded, so your Mac stops checking it. Typing a command you can't read, on the say-so of a stranger, is the exact behavior all of this exists to prevent.

Where to Get Mac Apps Safely

• The Mac App Store — highest trust. Apple reviews each app before it's accepted and signs it, and can pull it quickly if there's a problem. Look here first, every time.
• The maker's own website, address typed by hand — high trust. This is the normal way to get Chrome, Firefox, Zoom, and printer software.
• Your printer or scanner manufacturer's support page for your exact model — high trust. Not a driver-download site. And try the printer first: most work with no download at all.
• Search results marked “Sponsored” or “Ad” — low trust. Paid placement, where the lookalike sites live. Scroll past them.
• Download portals that “host” popular apps — low trust. They often bundle extra junk into the installer.
• Links in email, texts, or pop-ups — no trust, regardless of who they appear to be from.
• Cracked or pirated software — no trust. This is the single most reliable way to get Mac malware.
• One habit that prevents most of this: bookmark the download pages you use, the day you install each app. Then every lookalike site in the world becomes irrelevant to you.

The One Setting Behind All of It

Apple menu > System Settings > Privacy & Security, then scroll to Security. Under “Allow apps downloaded from” there are two choices. App Store allows only App Store apps and refuses everything else — reasonable for a Mac used for email, web and photos. App Store and identified developers is the default, and it's what most Macs should run; you need it for Chrome, Zoom and printer software. There used to be a third option, “Anywhere,” which turned the check off. Apple removed it from this screen years ago, and I'm not sorry to see it go — the per-app Open Anyway route does the same job one app at a time, which is the right size for that decision. If the setting is grayed out, Apple notes these options may be unavailable when a Mac is managed by a system administrator or IT department. On a work or school Mac that's expected. On a personal Mac nobody manages, it's worth a look at System Settings > General > Device Management for a profile you didn't put there.

Changed Your Mind? How to Undo an “Open Anyway”

1. Quit the app — right-click its Dock icon and choose Quit, or use Apple menu > Force Quit if it won't.
2. Drag it from Applications to the Trash and empty the Trash. If it came with its own uninstaller, use that instead — some apps put pieces where dragging won't catch them.
3. Check System Settings > General > Login Items & Extensions and remove leftovers with the app's name or the maker's on them.
4. Check browser extensions — Safari > Settings > Extensions, and the same in Chrome or Firefox if you use them.
5. Restart the Mac. Not optional — this is when macOS cleans up known bad software.
6. The exception you granted applies to that one copy of that one app. Once it's gone, the exception has nothing left to point at.

What's in the 27-page PDF

• What Gatekeeper is, in plain English — and the three things it checks before an app runs
• The whole guide in six checkboxes, plus the one sentence worth memorizing
• A table of every warning message, what it actually means, and which page to turn to
• App Store vs. identified developer vs. unsigned — the three kinds of Mac apps
• What “notarized by Apple” does and does not promise
• The Open Anyway flow step by step, including the one-hour clock nobody mentions
• Why the old right-click trick stopped working — and the Terminal commands to ignore
• The two messages that are not negotiable: “will damage your computer” and “is damaged”
• The five-question source test, and a ranked table of where to get Mac apps
• The safe install checklist for the refrigerator, plus .dmg vs .pkg and the password prompt
• The scams that live in this doorway, and how to undo an “Open Anyway” you regret
• Printers, old software and hobby tools; a page for family helping from a distance; Q&A, glossary and a fill-in cheat sheet

Why I wrote this

“It says my Mac won't open it — did I break something?” is one of the calls I get most, and the answer is almost always no. Nothing ran. Your Mac stopped and asked. What bothers me is the other direction: the warning is also the exact screen a scammer needs you to click past, and Apple's own guide says overriding security settings is the most common way a Mac gets infected. So this guide tries to do both jobs honestly — get a good app open in a minute, and make the bad moment easy to spot. I write these as printable handouts so the checklist can sit next to the Mac. If you'd rather have company for it, that's a flat $99 visit with a 30-day follow-up included. — Bill