One Bitcoin Group Now Controls 51% of Total Mining Power

extremetech.com

This is a great writeup. It's not as FUD-y as other's I've seen.

https://bitcoinfoundation.org/2014/06/13/centralized-mining/ is another good read. Where OP's link is more technical, this BCF link factors in the other side of things -- what would happen if someone actually did take advantage of this vulnerability.

Thanks for sharing that interesting link. He has a good point and ends with a wise standing:

However, this is a good time to re-iterate my standard disclaimers: Bitcoin is still a work in progress, and you should only risk time or money on it that you can afford to lose. Mining centralization is one of several potential risks; read Jim Harper’s excellent Risk Management Study for a clear-headed assessment of risks and consequences.

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