In Goblet of Fire:
Mad-Eye Moody was captured by Barty Crouch, Jr. and wasn't really teaching the Defense Against Dark Arts class at Hogwarts during Harry's Fourth year. Crouch impersonated him and taught in his place during that time.
With that in mind, and considering that Crouch was a Death Eater...
Was any of what the students learned or what Mad-Eye Moody said during that time reliable? Were the students given much in terms of misinformation?