Presuming you're talking about my take on ninja I'm informed mainly by martial arts lore, which (outside the schools calling themselves ninjutsu, which incidentally are almost all modern inventions) is probably a little more interested in demystifying the tradition than the Wikipedia authors are. The wiki definitely puts a more glamorous spin on it, but reading between the lines I don't see too much that's actually incompatible with my take -- note the emphasis on infiltration and sabotage rather than combat, and that the field agents were mostly drawn from the lower class.