Stealing attacking creatures

[sithantic]

Opponent declares attackers, {Stormbreath Dragon}, lets say. In response, I cast {Quicken}, and then {Act of Treason} targeting the Stormbreath. What exactly happens here? Is the dragon removed from combat? Is he still attacking me?

[MuggyWuggy]

He in under your control
If you do this before declare blockers step (response to declaring attacks)
You may now assign it to block any attacks left

[sithantic]

He in under your control
If you do this before declare blockers step (response to declaring attacks)
You may now assign it to block any attacks left

Yes, but will he still deal damage to me?

[Avnger345]

He in under your control
If you do this before declare blockers step (response to declaring attacks)
You may now assign it to block any attacks left

Yes, but will he still deal damage to me?

No because there is no attacker

[MuggyWuggy]

You've taken him before the blocker step,
So he is removed from combat and put under your control, what you do with him after is up to you

[Ekann1]

506.4. A permanent is removed from combat if it leaves the battlefield, if its controller changes, if it phases out, if an effect specifically removes it from combat, if it's a planeswalker that's being attacked and stops being a planeswalker, or if it's an attacking or blocking creature that regenerates (see rule 701.12) or stops being a creature. A creature that's removed from combat stops being an attacking, blocking, blocked, and/or unblocked creature. A planeswalker that's removed from combat stops being attacked.

Here's the ruling.