The Spider's Web (Mirkwood Nighmare): When Revealed: The player with the highest threat exhaust all heroes he controls. Then, attach this card to one of that player's heroes...
...if i have all my heroes exhausted (for example, commited), i mustn't attach that nasty card to anybody, isn't? Nice!!! (for example, if you see it is coming by Denethor, i will exhaust all my heroes before it is revealed)
I don't think so. That would mean that if only one hero is exhausted when you draw that card, you cannot exhaust all heroes. So if a hero is already exhausted, you cannot exhaust him, but he still qualifies as being exhausted.