What is Gatekeeper?

Since version 10.8, Mac OS X features the so-called "Gatekeeper" security mechanism, which prevents installations from dubious developers. While this might be a move to increase the security and reduce malicious software infections on end-users computers, all applications are required to be digitally signed with an Apple Developer ID and thus each installer must be recompiled by the developers. If an application is unsigned or its signature is outdated, for example since Mac OS X has been updated, Gatekeeper will simply block the installation and warn the user about the unidentified program.

Which applications are affected?
All Steinberg application installers and updaters, which are downloaded from the Internet and then run from your local hard disk are directly affected, therefore requiring workarounds as described below.
Steinberg installers run from CD or DVD are not affected.

Workarounds for Steinberg applications
Fortunately enough, there are two simple workarounds to install unsigned programs:

1) The temporary workaround

• Hold down the "Control" key (ctrl) on your keyboard and click the installer package.
• Choose "Open".

Please note that the temporary workaround may not work properly in case you are not installing from a DVD, but from a downloaded DMG image AND the application is meant to be installed via the Start Center. If the Start Center is not run from DVD, Gatekeeper will kick in and any application installer initialized from the Start Center will therefore fail. In this case, the workaround is to avoid installing the application from the Start Center, by running the installer packages directly with the method mentioned above. The MPKG installer packages are included in the DMG and are usually located in a sub folder called "Application name Mac OS X". If in doubt, disable Gatekeeper permanently like described below.

2) The permanent workaround (not recommended)

• Disable Gatekeeper altogether by opening the System Preferences
• Click on "Security"
• On the "General" tab, enable the option "Anywhere" under "Allow apps downloaded from:"