How to fix “This file is damaged and can’t be opened” in Mac OS X

Yesterday I was trying to open an installer which was offered as a .dmg file. That’s a disk image which mounted itself fine, but when I ran the installer contained in the disk image, all I got was an error message: “ZBrush to Keyshot Content Installer is damaged and could not be opened”.

At first I thought perhaps the download had a problem, or perhaps the source file was corrupt. But in such cases the .dmg usually doesn’t even mount – which mine did. Perplexed, I raised a support ticket with the provider of the software.

Thanks to Matthew at Pixologic support I received a very quick solution to this puzzle: there’s nothing wrong with my download, nor with the source file – it’s OS X’s Security Settings that flag up an inappropriate error.

Thank you, Gatekeeper!

Here’s how to fix it:

• head over to System Preferences – Security and Privacy
• select the General Tab
• click the little Lock Icon and enter your password
• now select Allow apps downloaded from anywhere

I would have never made the connection between the “corrupt file” error message and Gatekeeper preventing the file from opening properly. Usually when Gatekeeper gets involved it’s very clear that OS X is preventing something from being opened, with a hint of where to tweak those settings. But not in this case.

As soon as you select “Allow from anywhere” a modal window pops up asking you if you’re really sure. It also explains a new Yosemite behaviour that if you decide to go ahead, the setting will revert back in 30 days. So if you think “hey, I’ve tweaked this setting recently”, don’t doubt your sanity.

There’s no need to download the file again either. Now my download opens fine, mounts fine, and most importantly installs fine too.