Enchanted creature gets -1/-1, and its activated abilities can't be activated.
When Ulamog attcks is that an activated ability or or is it a creature spell that can be countered?
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It is neither. It is a triggered ability:
603.1. Triggered abilities have a trigger condition and an effect. They are written as “[When/Whenever/At] [trigger condition or event], [effect].”
Viper's Kiss has no effect on any of these abilities. It will give Ulamog -1/-1 making it a 9/9, but Ulamog will still exile cards.
Spells are only ever cards (or copies of cards) that are on the stack. Abilities never count as spells.
Activated abilities also have a specific formatting you can recognise them by:
602.1. Activated abilities have a cost and an effect. They are written as “[Cost]: [Effect.] [Activation instructions (if any).]”
An example of activated abilities is found on Elvish Mystic: note the presence of a cost (tap Elvish Mystic), colon :, and effect (add green mana). An activated ability has all three of these; an ability without these is not an activated ability.