By default, your Mac's security settings only allow installations from developers registered through Apple's developer identification protocols, so most installations from the internet will cause a message like this to be displayed:
"ALL In Learning Installer.pkg' can't be opened because it is from an unidentified developer. Your security preferences allow installation of only apps from the Mac App Store and identified developers."
It's easy to allow the installation:
Open Finder and go to the folder the installer was downloaded to. By default, in Chrome for Mac, the location will be: "Users/[your username]/Downloads"
Hold down the Control key and click on the application. In the menu that pops up, click "Open."
- A window will pop up asking you to confirm. Click "Open."
Alternate steps to allow all installations from unidentified developers from now on:
Warning: While this increases convenience, it can also increase the chance that malware may get installed.
Go to the Apple Menu (upper left of your screen), choose System Preferences, click Security & Privacy, and select the General tab. Then, click "Click the lock to make changes."
Enter your username and password into the prompt that appears and click Unlock.
For OS 10.12 and up, click "App Store and identified developers." Then choose "Open Anyway." You will be able to install applications downloaded from the internet for 2 hours and then settings will revert.
For older versions of OS 10, click "Anywhere" and then on the prompt that appears, click "Allow From Anywhere."
Exit System Preferences by clicking the red button in the upper left of the window. You should now be able to install applications downloaded from the internet.
For more information, see Apple's Knowledge Base Article: http://support.apple.com/kb/HT5290.
Additional keywords: untrusted trusted