51% - Blockchain & Bitcoin 101 / Categories / Bitcoin Basics / PoW and Integrity

at about 6:37 in the video i think Ivan explains that you can’t change block data unless you have 51% or more of the hashrate and even after you are able to make the changes ounce you have said hashrate. You would then have to outpace other miners to catch up and be able to add the modified block to the chain.

Do i have that understanding correct? Could someone help break that down for me if i don’t have that correct. Thank you.

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You are correct. That is what we call a 51% attack. Ideally you would want to have more than the 51% of the hash power. Doing this on the bitcoin network would be quite expensive due to the total hashrate the network has. The further you go back the more expensive it would be. Its simply not worth it. Keep in mind that you would need a ton of equipment and you would need a ton of power to make something like that happen. That’s why many people agree that POW (Proof of Work) is the most secure consensus we have right now. It is connected to real world, with energy. Keep up the great work. :slight_smile: