Recently stuck with the following error message when in installing third party apps on macOS Sierra. "Application" is damaged and can't be opened!
Apparently, the issue lies with "Gatekeeper"
The Gatekeeper settings can be found in System Preferences > Security & Privacy > General. The Gatekeeper options are located beneath “All apps downloaded from:” with the choice of “Anywhere” missing.
Thankfully, the “Anywhere” setting can be restored to Gatekeeper in Sierra with a Terminal command. First, quit System Preferences if it’s open and then open a new Terminal window. Enter the following command, followed by your admin password when prompted:
sudo spctl --master-disable
Now, relaunch System Preferences and head back to the Gatekeeper settings. You’ll now see that “Anywhere” has been restored. Click the padlock in the lower-left corner to enter your password and make changes, then select “Anywhere” from the list of Gatekeeper options. The security feature will no longer bug you about apps from unidentified developers.