"Identical" DMGs: one installs, one does not We've got a DMG from a vendor that we put on our web server for download. After download, the file on my Mac (OSX 10.10.1) is identical to the original file (did a hex compare), and the DMG mounts fine... but the installer inside the DMG will not work after download.

To put it a different way, I have two seemingly identical DMG's, both of which mount, but only one of which will actually run the installer in the image, once mounted.

The permissions were slightly different between the two DMG's after download. Changed them so they are now identical.

We've tried this on three Macs with at least two versions of OSX, and the results are the same.

What else could be wrong? Is there anything in the OS security settings that could have saved some information about the file having come from the internet and blocking the installer somehow? If so, where?
There is information in extended attributes.

What is the setting in Preferences/Security &amp; Privacy/General "Allow apps⋯"?

This needs to be set to an appropriate value to allow non-App Store apps to be opened.