Somewhere I've read that one just needs 1/3 of total hashing power to gain control over the network. He withholds a selfmined valid block until he recognize another one publishing "his" block, then releasing "his" one gaining a time benefit. He lets all other participants mine "his" block while he's mining a new valid one, therefore gaining control over the blockchain. Dunno the exact details and it's been a while since I've read about that issue but I find it quite scary. The part I don't get is how he should be able to publish "his" block after another one does and still "wins". Maybe this is old news and has already been fixed, would be nice if some tek could drop a line on this. Thanks.