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Sybil Attack

Sybil attacks are a type of attack seen in peer-to-peer networks where one operator, or node, in the network controls multiple identities at the same time in an attempt to undermine / overthrow the authority of the rest of the nodes in the network. The main goal of this attack is to take over a network so that they can do illegal or unauthorized activities without needing authorization. 

In Bitcoin, the proof of work consensus algorithm secures the network from Sybil attacks. Since so much work (and cost) is required for mining a block, honest miners are more likely to be rewarded with the block reward than nefarious ones are. It’s also extremely unlikely that nebulous miners would have enough hash power to control 51% of the miners since there are so many miners around the world and the hash rate is so high and/or constantly growing.


  • A 51% attack on Bitcoin is a classic example of a sybil attack. 
  • Creating fake reviews on Yelp, Amazon, or other review based businesses by one entity.
  • Situation where one user creates hundreds or thousands of fake social media accounts to influence an election, like a post, or share material unethically. Note: if the social media platform isn’t itself compromised, then this falls under pseudo-Sybil attack.