What is Sybil Attack


In a Sybil attack, a malicious individual creates multiple fake identities or nodes in a blockchain network to gain undue influence and control. The attacker can use these numerous false identities to manipulate the network, disrupt its functionality, or carry out other malicious activities.

The term "Sybil attack" originates from the book "Sybil," a case study about a woman with dissociative identity disorder, reflecting the attacker's creation of multiple fake personas.

Sybil attacks can target various consensus mechanisms in blockchain networks, such as Proof of Stake (PoS) or Proof of Authority (PoA). The attacker aims to gain control over a significant portion of the network, which can have severe consequences. For example, the attacker could refuse to transmit or receive blocks, effectively blocking users from accessing the network. Additionally, Sybil attacks can facilitate subsequent 51% attacks, in which the attacker controls the majority of the network's resources, allowing them to manipulate transactions and double-spend.

What is a 51% attack? What's its mechanism? Please refer to the content: What is 51% Attack

In the context of cryptocurrency airdrops, Sybil attacks also pose a significant threat. Airdrops are events where tokens are distributed for free or in exchange for a small task to a large number of users, often to promote a new project or reward existing users. In a Sybil attack targeting airdrops, an attacker creates numerous fake accounts to claim multiple portions of the distributed tokens, unfairly benefiting from the airdrop at the expense of genuine users. This attack undermines the primary purpose of airdrops, which is to encourage widespread adoption and equal distribution of tokens.

Past Attacks

One historical instance of a Sybil attack occurred in the Ethereum network in 2016. This attack exploited the Ethereum network's peer-to-peer (P2P) layer, causing performance issues and delaying transactions. The attacker created many nodes to flood the network with fake transactions, which overwhelmed the system and caused disruption. In response, the Ethereum community implemented changes to the network protocol to mitigate the effects of this type of attack.

Protections from Sybil Attack

To defend against Sybil attacks, blockchain networks employ various strategies. Proof of Work (PoW) consensus mechanisms, used in networks like Bitcoin, make Sybil attacks more expensive and complex by requiring significant computational resources for an attacker to control most of the network's nodes. However, PoW networks are still susceptible to 51% attacks, especially if they are relatively small and have limited resources.

An alternative approach is the Proof of Activity (PoA) consensus mechanism, which combines elements of both PoW and PoS systems. In PoA, the mining process begins like a PoW system, but after a new block has been successfully mined, the system transitions to resemble a PoS system. This hybrid approach requires attackers to have an advantage in hash power and staking proof, making Sybil attacks considerably more costly and challenging.


In conclusion, a Sybil attack is a significant cybersecurity threat in cryptocurrencies, wherein an attacker creates multiple fake identities to gain control over a network. Blockchain networks use consensus mechanisms, such as PoW, PoS, and PoA, to counteract these attacks and secure their systems. Various verification processes can help mitigate Sybil attacks in airdrops, promoting a fair distribution of tokens and ensuring a healthy ecosystem for both beginners and experienced users.

You might also be interested in the following content:


Security Incidents

What else do you want to learn?


In This Article

Use TokenInsight App All Crypto Insights Are In Your Hands