Snow Enchantment - Aura, W (1) Enchant creature Enchanted creature can't block and its activated abilities can't be played. {S}: Enchanted creature gains defender until end of turn. ({S} can be paid with one mana from a snow permanent.)1
Illus. Alex Horley-Orlandelli
Static and triggered abilities still work. [Coldsnap FAQ 2006/06/14]
It will not stop a creature from attacking unless the ability is played before attackers are declared. Giving a creature Defender after it is already an attacker will not stop it from attacking. [Coldsnap FAQ 2006/06/14]