How do I add an identified developer to the list of allowable downloads e.g. updates to Open Office?

My security settings in preferences allow app downloads from Mac app store and identified developers. I have downloaded an update to Open Office and when I try to open it I get a message that the OpenOffice.app can't be opened because it not from an identified developer (sourceforge.net?). When I authenticate and click on "open anyway" it doesn't open it anyway and gives me the same error msg ("not from an identified developer"). I can't find bubkis about how to add an identified developer so this doesn't happen again. Meanwhile, I can't use OO. Very frustrating...