This message seems to appear for some customers who have bought iBank 5 from the Mac App Store. It is happening because Apple has an expired certificate. It isn’t an issue with IGG. The full message reads:
“iBank 5” is damaged and can’t be opened. Delete “iBank 5” and download it again from the App Store.
DO NOT DELETE YOUR iBank DOCUMENTS! If you delete your documents you will be deleting your data. If you delete the application, all of your data will be left untouched.