I don't understand how someone can beat the zombie horde as they defend together in an engagement!
So in a way you must have more than 8 in attack to give it a wound... is this wound applied to the zombie copied ? what happens to the horde when someone remove (I don't know if it is possible) the copied zombie?
You can't target the specific zombie because it becomes part of the horde. There are ways, however, to beat it. To begin with, remember that it's only as strong as your opponent's hand. If your opponent plays out a lot of cards on his or her turn, that weakens the horde. Sometimes, as a defender, you can use the horde to your advantage. You can use the sniper rifle to force your opponent to discard a card. During combat, you can use the shotgun (please check shotgun errata) to force the opponent to discard 2 cards. Ultimately, the best defense against a zombie horde (aside from Wilfred and Moose together), is a Molotov Cocktail, which will kill every zombie in the horde, forcing your opponent to discard his or her entire hand, the horde, and the attached zombie.
In future editions, the rulebook will contain a section for "hordes" and the horde cards will only include text that makes each one unique.