I think I've seen this talked about before, but I can't find it anywhere in the FAQ or the Rules Summary. If there is an effect that forces both players to assign indirect damage, or each corrupt a unit. Who has to do it first? The player who played the card, or the opponent?

For combat damage, the attacker assigns first. For 2 forced effects occurring simultaneously, the active player has priority. So I would assume the player that controls the effect has to assign his indirect damage first, but I can't find a ruling on it anywhere. Anyone have one?

Nevermind. Google is my friend even if the FFG forum search isn't. I found an explanation from Dormouse on BGG.

The person whose action/response is being resolved always makes all decisions first, so yes you assign all your damage and then your opponent does in this case. ... it is an extrapolation of the basic rules. When you trigger an effect you must pay all costs and choose all targets before the effect resolves, that would include which units would be targeted. Since the effect does not specifically state that your opponent must first it does not contradict the basic rules concerning triggering an effect there is no "golden rule" situation.