This is an issue introduced by the default security settings of Mac OS X 10.8+ (Mountain Lion), which allow only applications downloaded from "Mac App Store and identified developers". The alert is highly misleading.

Solution 1:
Change the setting in the "Security & Privacy" preferences (Apple menu > "System Preferences..." > "Personal" section > "Security & Privacy" > "General" pane) to "Anywhere", you should be able to run AccuBarcode Pro Installer and get the software installed on your Mac without any problems.

This affects your general settings. If you feel that your "Security & Privacy" should be set back, do this after the installation.

Note: If you are using Mac OS Sierra(10.12+), maybe you need do the following steps first

1. Disable Gatekeeper in macOS Sierra
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.

2. Restore Sierra Gatekeeper Settings to Default
If you’ve enabled the “Anywhere” option by using the Terminal command above and later want to remove it, you can head back to Terminal and run this command instead:

sudo spctl --master-enable

This way, you can ensure better security for any new users of the Mac.

Note: Threre are two '-' before 'master'.

Solution 2:
You can also right-click on (or hold the Control key and click on) Accubarcode Pro Installer and choose "Open" from the popup menu, that will bypass the Mountain Lion app source security policy and execute it normally.

The app Accubarcode Pro Installer will be stored as an exception to your security settings, and you will be able to open it in the future by double-clicking it. This doesn't override your general settings.