I get the “App is damaged, cannot be opened. You should move it to the Trash” message from time to time on my iMac. It mostly involves Apps from the Mac App Store. There are things that can be done to remedy this problem. This article lists some things to try to fix the “damages App” message. Usually, just a Deletion and Reinstall of the App works for me, but there are some other things you can try. Check out the article.