App can't be opened because it is from an unidentified developer

Question

It's because of the Security options.

Go to System Preferences... > Security & Privacy and there should be a button saying Open Anyway, under the General tab.

You can avoid doing this by changing the options under Allow apps downloaded from:, however I would recommend keeping it at the default Mac App Store and identified developers.

An easier way to open a document from an unidentified developer, if you know it's safe, is to control-click on the file icon and then select "Open." You will then be given the option of opening it regardless of its unidentified source.

Right-click (or control-click) the application in question and choose "Open"

You can also use the xattr command as in Stack Overflow question How do I remove the "extended attributes" on a file in Mac OS X?.

Just remove the com.apple.quarantine attribute. It works even if you don't have an administrator account, which can be a plus. After that, the app isn't considered "downloaded" and is therefore not blocked.

In terminal type the command:

xattr -d com.apple.quarantine [file path here]

Once you click enter it will no longer have that problem. Its annoying that apple adds a quarantine to files automatically. I do not know how to turn this off but there probably is a way...