Even without that collusion, if you control 40% you still have a high probability of pulling off a double-spend attack. My recollection (sorry, I don't have a

Even without that collusion, if you control 40% you still have a high probability of pulling off a double-spend attack. My recollection (sorry, I don't have a link, so I might be wrong) is that someone somehow associated with GHash.io already pulled something like this off when they were still below 30%