Well in theory this sort of thing should only be possible with a mod (which everyone muse have installed) or through exploiting a bug in the game.
Well no, that's wrong. The point I was trying to make in my original post is that just because something is peer to peer doesn't mean it's imune to hacking.
If I attack you and on my machine I do 1,000,000 damage and on your screen I do 250 damage it will cause a desynch cause on mine your dead, on yours you're not.
But if on my machine I buy something and my machine checks I have enough gold, if I hack to say I've got 1,000,000 gold I can buy it, then my machine tells all other machines I just bought the 'I WIN' button they probably don't actually check that I had enough gold in the first place.
Wouldn't cause a desynch.
Other cases I can think of a possible vulnerability is hacking favor points (not a big deal), showing extra stuff on the interface such as CDs and mana of others, potentially using items that you don't own such as teleport scrolls.
Just because it's peer to peer doesn't mean it's imune to cheating in these areas, each client will need to check the actions of all other users.
Complete immunity would only be caused by the only information sent between peers are key and mouse presses and each one working out their own game from that. I doubt this is the case because it's seriously hard to write.
Getting other users mana and the like will never be immune.