Quote from: butka on September 03, 2018, 10:18:42 AM

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How big? Probably at least 50% of hashrate, which is why it was never observed in practice and possibly never will. BTW selfish mining can be easily detected by the increased number of orphaned blocks.

With 50% of the hashrate you're not Selfish Mining anymore; you're effectively able to take over the network since you now can outrun the other miners indefinitely.

Selfish Mining only requires you to outrun your competitors, say, 2-3 blocks at a time. For that you don't need quite as much hashing power. By itself it's not really much of a threat though (apart from causing low-confirmation-count transactions to be unreliable); it's when used as part of a larger plot to either bankrupt your competitors or force them to collusion that Selfish Mining becomes dangerous.