Crypto glossary
Selfish mining
Selfish mining is a strategy in which a miner withholds the blocks it finds and releases them tactically to earn more than its fair share of rewards.
Described by Ittay Eyal and Emin Gün Sirer in a 2013 paper titled Majority Is Not Enough, selfish mining works like this: a miner that finds a block keeps it private and keeps mining on top of it. When the honest network finds a competing block, the selfish miner publishes its own to win the race or to cause the honest block to be orphaned. Honest miners waste work on blocks that end up stale.
The paper showed that, under some network conditions, a pool with around a quarter to a third of total hashrate could earn a disproportionate share of rewards, and that rational miners might then join it, pushing it toward a majority. The finding challenged the assumption that Bitcoin is safe as long as no one controls 51% of hashrate.
There is little evidence of sustained selfish mining on Bitcoin. It is detectable through unusual patterns of orphaned blocks, it hurts the attacker's reputation and the coin's price, and its profits depend on how well the miner is connected to the network. Still, it remains a standard example of how incentive design can fail and is studied for proof-of-stake systems too.
Example
A pool with 30% of hashrate finds two blocks in a row and keeps them secret; when another miner publishes a block, the pool reveals both, its longer chain wins and the other miner's block is orphaned.