In your OS X adventuring you may come across this message:
“Application Name” is damaged and can’t be opened. You should move it to the Trash.
Fortunately, there’s a giveaway. The icon shown is the Security & Privacy icon. Go to your prefs, to Security and Privacy and in the “Allow apps downloaded from:” set to Anywhere.
Now try relaunching the application. It should launch now.
Then go back to your security and privacy and set it back to “Mac App Store and identified Developers” (if it wasn’t set there before, you really should. Some of the best apps aren’t in the Mac App Store)