Whether or not Johann Georg Hiedler was actually the biological paternal grandfather of Hitler may remain unknown as he was not recorded originally as the father on Alois's birth certificate. Illegitimacy was common in lower Austria; in some areas it reached as many as forty percent of births and as late as 1903 the rate was twenty-four percent, with the children normally legitimized at a later date. Hitler's ancestry was questioned when his opponents began spreading rumors that his paternal grandfather was Jewish, since one of Nazism's major principles was that to be considered a pure "Aryan" one had to have a documented ancestry certificate ("Ahnenpass").