Oracle Text

Prevent all combat damage that would be dealt by non-Werewolf creatures.

Whenever you roll H, each creature you control gets +2/+2, gains trample, and becomes a Werewolf in addition to its other types until end of turn.

Card Rulings

6/1/2012 A “non-Werewolf creature” is a creature that doesn’t have the Werewolf creature type. A creature with additional types, such as a Human Werewolf, is not a non-Werewolf creature.
6/1/2012 Creatures that you gain control of after the chaos ability resolves won’t get any of that ability’s bonuses.