This is as good a place as any to ask this question. Do we actually know how many large mining groups we need to make up 51% of the processing power of the block chain (hopefully that make sense, from my understanding of bitcoin). There has been a number of changes to the bitcoin protocol, which have been made in a short amount of time and unanimously, from what I can see. That implies to me that bitcoin is in practi…
Two. GHash.io and BTCguild make up 27% each, for a total of 54%.
GHash.io had actually been acting maliciously according to some users on Bitcointalk, but the operator claims that was a rogue actor inside that has been dealt with. Double spends against betting sites in particular were involved with this one.