It's widely accepted that versions after 7.6 are all full of holes, buggy and easily exploitable due to the FCK editor being implimented in core code. Ravennuke is the last stable version of phpnuke (7.6) with the vulnerabilties, exploits and holes closed. You will also have a hard time finding in depth support for phpnuke versions higher than 7.6 due to the overwhelming problems with it, in fact, many sites no longer even respond to tech. related questions on higher versions.