This short video breaks down the 51% attack: what it is, what an attacker can and cannot do, and why pulling one off against Bitcoin is economically irrational. Below you'll find the full transcript and FAQs. For a deeper look at how Bitcoin's security model prevents this scenario, read the full written guide on 51% attacks.
Read the full guide: What is a 51% Attack?
Full Transcript
Ever wondered about a 51% attack on Bitcoin? Let's take a closer look.
A 51% attack occurs when a single entity controls over 51% of Bitcoin's hashrate. This could enable them to censor or reverse transactions and mine empty blocks to disrupt the network. But it cannot change Bitcoin's rules or steal coins. Miners still have to work within the rules enforced by node operators.
So is it feasible? It's possible, but extremely foolish. It would require immense computational power costing billions of dollars, something only a nation-state could potentially achieve. Even then, the network's structure makes it difficult for attackers to sustain control indefinitely.
In such a scenario, transaction fees would surge, attracting honest miners to include transactions.
So why can't the US kill Bitcoin by printing money and buying ASICs? Because the benefits would be small and temporary, while the risks would be serious and lasting. Imagine the headline: a nation-state hyperinflates its currency and still fails to stop Bitcoin.
Bitcoin wins in the end.
FAQs
What does "51% of the hashrate" mean?
Hashrate is the total computing power used to mine Bitcoin. Controlling 51% means one entity runs more mining hardware than every other miner on the network combined. That majority position would let the attacker decide which transactions get confirmed and which don't.
Can a 51% attacker steal Bitcoin from your wallet?
No. A 51% attack gives control over block production, not private keys. The attacker can reverse their own recent transactions (enabling double-spends) or block others from confirming. They cannot move coins they don't own. Bitcoin's cryptographic rules still apply.
Has Bitcoin ever experienced a 51% attack?
Bitcoin itself has never been 51% attacked. Smaller proof-of-work networks with low hashrate (like Bitcoin Gold and Ethereum Classic in their earlier forms) have been hit. Bitcoin's massive global hashrate makes the cost prohibitive at a scale no other network matches.
How much would a 51% attack on Bitcoin cost?
The cost changes with network hashrate and hardware prices. Estimates put the figure in the tens of billions of dollars for hardware alone, before accounting for electricity, logistics, and the ongoing cost to sustain the attack. The economics only get worse for the attacker over time.
Why would a nation-state attack fail?
A government would need to acquire and deploy more mining hardware than the rest of the world combined. Even if it succeeded briefly, honest miners would have a massive economic incentive to rejoin and reclaim majority hashrate. The attacker would also crater confidence in the very currency it spent billions to acquire. The game theory doesn't work in the attacker's favor.
What role do Bitcoin nodes play in preventing attacks?
Nodes enforce the protocol rules. Even if an attacker controls 51% of the hashrate, they cannot create coins out of thin air, change the supply cap, or bypass signature verification. Nodes would simply reject any blocks that violate the rules. Hashrate controls block ordering, not Bitcoin's consensus rules.
By Josh Heine, Content Strategist at Simple Mining
Published: August 12, 2024
Modified: March 9, 2026