Japanese advanced-level ninja knowledge exams held

http://the-japan-news.com/news/article/0001391808

Meanwhile a new authoritative ninja text book has been released:

Publisher Kasamashoin has released “Ninja no Kyokasho” (The Ninja Textbook), a volume filled with the history and art of ninja. The book was compiled under the supervision of Yamada Yûji at Mie University, a top ninja researcher.

At the risk of being assassinated ...

After living through the ninjutsu 'boom' of the 1980s, I was told recently that ninja were a relatively modern phenomenon with an invented history, etc, mainly for marketing purposes. Does anyone know how authentic ninja are in Japan's past?