Destruction player declares zone they are attacking and names attackers, including a Clan Rats. Then, in the action window that follows, (or for the defender's window), uses the Clan Rats ability to pump up a Skaven. As they had already been declared as an attacker, they would still get to attack. Is this correct?

Does corruption prevent attacking or does it just prevent a unit from being declared as an attacker or defender?

Yes, that is correct. If a unit is corrupted after it is already declared as attacker, it is still going to apply/assign damage.

That's what I thought. Others have pointed to the last part of the second sentence of the second paragraph of the Coruption rules that seem to imply that cards lose the ability to attack or defend once corrupted:

"Some cards become corrupt when they use an ability.
Other effects can corrupt an opponent’s forces,
thereby preventing those forces from attacking or
defending."

Those quotes don't preclude the interpretation I have given. Corrupted units cannot attack or defend, but they can inflict damage if they are already attacking/defending.

It is sort of like M:tG, if you've played that:

If a creature is declared as attacking you, and you play a card that taps it, the creature is still attacking.

Can you play a tactic in response to someone declaring a unit as an attacker? If this is the case, wouldnt actions then resolve in reverse order ie unit is first "tapped/corrupted" and then that unit is unable to be declared as an attacker., so the "declare attacker" action fails.

For even more fun, combine this with the new Abandoned Mine!

1. Use Abandoned Mine at the very beginning of your turn

2. Respond with the Clan Rats, pumping power

3. Continue to your "Un-corrupt" step, and restore the Clan Rats you just used to pump power!

@mateooo: Is "Declaring attackers" an action which can be responded to? There's definitely a window after it has been completed, but I'm not sure if it counts as an action in and of itself, so it may not be respondable.

You may only respond to actions and nothing in the rulebook says declaring attackers is player action, so I'd say no. Notice how in the Capitol Phase they specifically say playing a unit, support, or quest is considered taking an action, which lets us know it is something that can be responded to, as well as each time one card is played your opponent(s) get a chance to take an action in response prior to you being able to take another action.

You can't play tactics DIRECTLY in response to someone declaring attackers. BUT in the rulebook (page 12, bottom left) there IS an action window right after attackers are declared.

PeekItUp said:

while this is true it does not mean that playing a corrupting effect in that action window will now corrupt a previously declared attacker. Cards only stack when there actions played in response to other actions.

RexGator said:

I think you mean it will corrupt a previously declared attacker, it just won't prevent that Unit from attacking (since already declared) or remove it from the attack.

You are correct Dam, that is what I meant to say!