From the wiki page I linked:
It is possible for someone who has been Imperiused to place others under the curse as well.
whilst under the caster's control, the curse may also endow the victim with whatever skills that are required in order to complete the task at hand, such as increased strength or allowing them to cast spells far above their level.
Resisting the Imperius Curse is possible, but requires great strength of will and character.
Some can resist, but they could be defeated by a combination of 1) the archwizard at the head of the network and 2) his army of slaves.
Actually, if the Imperius Curse grants the victim the abilities necessary to carry out tasks (which I had also forgotten about,) then it seems more likely to me that it would actually require some degree of micromanagement from the end user for every step in the chain. It makes it seem more like they're actually investing some of their own mental power rather than just applying some suggestion, and there should only be so much of that to go around, which could make creating an army of imperiused slaves an impossibility.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 88-89. The previous thread has passed 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: