macOS Quarantine

Files downloaded by macOS are tagged with an extended attribute com.apple.quarantine which will block applications from being launched.

On earlier macOS versions it was possible to use a right-click to bring up a dialogue that could bypass the quarantine.

Later version of macOS simply block access when the attribute is present.

This attribute can be removed by launching Terminal and entering the command

xattr -dr com.apple.quarantine file

This will remove the attribute from a file, or application, or all contents of a directory. Access will then be permitted unhindered.

MacOS Quarantine