The 51% attack is a very real and serious threat to the operational stability and transactional integrity of many decentralized blockchain systems. This type of malicious manipulation is a security threat that is mostly aimed at and works best against blockchain networks that use the Proof-of-Work (PoW) consensus mechanism.
It happens when one person or a group of people working together gets control of more than half (51% or more) of the network’s total hashing power. This lets them control the order of transactions and block finality.
Decentralization is what keeps a blockchain network safe. It stops one person or group from taking over and deciding what happens on the blockchain.
By illegally consolidating disproportionate power and control into the hands of one actor or collective, a successful 51% attack in blockchain essentially violates the system’s fundamental tenet of decentralization.
The attack is called that because it needs more than half of the network’s control to take over and change the way transactions are checked. Join us in this blog as we explore further into details of 51% attacks!
How Does a 51 Attack Work?
A 51 attack starts when one person or a strategically unified group takes control of most of a blockchain network’s processing power. This important level of dominance means being in charge of the network’s hashing power or mining hash rate.
The attacker can get around the consensus mechanism that checks transactions and adds new blocks to the chain because they have most of the computing power. The attacker then carries out the attack by doing a number of bad things that are important:
- Stopping Transactions: They can stop new transactions from being confirmed, which stops payments between users and causes a denial-of-service (DoS) attack on the network.
- Secret Mining: They start mining a private, different version of the blockchain in secret and keep the mined blocks from the rest of the network.
- Chain Release: This private chain grows faster than the honest, original chain because it has most of the hash power. When the attacker sends out their longer, changed chain to the network, the consensus rule says that all nodes must accept the longest chain as the right one.
This process makes the network throw away the most recent transactions from the original chain, which effectively changes the transaction history for the time of the attack. They can even block the addresses of honest miners to stop them from getting back control of the network, making sure that the attacker’s bad transactions stay on the network.
What Is 51% Attack Example?
The security of a 51% attack in blockchain is very weak when the network is large. This exploit has worked many times on smaller cryptocurrency networks with lower hash rates, but it is very unlikely to work on larger, more established networks like Bitcoin because it costs too much and requires too much computing power.
Smaller networks are much more at risk because it costs a lot less to rent the computing power they need, especially when they use cloud mining services like NiceHash. This makes the initial hardware investment cost much lower, which makes a 51 percent attack a financially viable threat for bad actors.
Sadly, there have been many major events in the history of digital assets where the 51% attack exploit has been successfully used against different blockchain networks, such as:
- Bitcoin Gold (BTG): In May 2018, a major security flaw in the BTG network let an attacker use the network to make fake double-spending transactions. Since then, the currency’s lower hash rate has made it easy for attackers to hit it often, which has hurt its reputation in the market.
- Ethereum Classic (ETC): This blockchain has been hacked several times, but the most serious hack happened in August 2020, when a bad actor completed a double-spend transaction. Several successful 51% attacks have targeted the network since 2019.
- Vertcoin (VTC): Even less well-known projects were vulnerable. For example, Vertcoin was hit by a 51% attack in December 2018, which showed how risky networks with low hash rate security are.
Between 2019 and 2020, the MIT Digital Currency Initiative found more than 40 chain reorganizations (reorgs) on smaller coins. These are often a sign of a 51% attack. These attacks in the real world show that the threat is real and not just a theory.
They also show how important it is to always be on guard and have strong security measures in place. Financial services often need more than one layer of security. For instance, Jeton has advanced security features to keep users’ money safe.
What Is 51% Double Spending?
The most sought-after and damaging result of a successful 51% attack is the ability to double spend money fraudulently. It means spending the same cryptocurrency coins more than once in a dishonest way.
The attacker’s ability to reverse transactions is what makes this possible. This is the main goal of a 51 attack. The attacker starts by doing something legal, like sending coins to an exchange or paying for a service. Then, they wait for the transaction to be confirmed on the public blockchain. For example, an attacker could buy something with 10 BTC.
At the same time, they use most of their hash power to mine a hidden, parallel version of the blockchain that doesn’t include that payment transaction. This makes it look like the transaction never happened.
The attacker makes their longer, fake chain public after they get the goods or service. The network accepts this longer chain, and the accepted history no longer shows the original transaction.
This lets the attacker keep the original coins and spend them again, which is how they successfully achieve 51% double spending and ruin the transaction ledger’s integrity.
Can a 51% Attack Reverse Transactions?
Yes, a 51% attack lets the person in charge undo recent transactions. The attacker can change the order of the blocks in the blockchain’s history by changing the network’s consensus mechanism, which is the “longest chain rule.”
This ability to undo transactions is what makes 51% double spending possible. The attacker makes the network reject some confirmed transactions by replacing the real part of the blockchain with their longer, privately mined chain.
This ability to reverse things undermines the blockchain’s basic immutability while the attacker is in charge. A successful 51% attack gives the attacker a lot of power over new transactions, but it is still very hard to change historical blocks, which are the transactions that were permanently confirmed and sealed into the blockchain before the attack started.
Transactions that have just been confirmed and don’t have many more confirmations on top of them are the most likely to be reversed. This lets the attacker change the history of transactions and stop them from happening.
What Is the Effect of 51% Attack?
A successful 51% attack has very bad effects, such as hurting the reputation and finances of the cryptocurrency network that was targeted. In addition to the immediate financial fraud caused by double-spending, the attack has a big effect on the trust and integrity of the network.
The market value of the cryptocurrency that was affected is likely to see a lot of price swings and maybe even a crash as trust in the currency falls. The attacker can stop or block new transactions from being confirmed by other users, which effectively stops payments and causes a denial-of-service (DoS) attack on the network.
A successful 51% attack shows that a lot of power is concentrated in one place, which goes against the blockchain’s main idea of decentralization and has an impact on network governance.
This ripple effect goes beyond the network that was affected and changes how people around the world see the security of blockchain technology. Bitcoin and other big networks are very safe because it costs a lot of money and energy to get 51% attack power.
Has Bitcoin Ever Had a 51% Attack?
No, the Bitcoin blockchain has never been successfully attacked by 51% of its users. Bitcoin’s huge size, the money it makes, and the fact that so many people are involved make it almost impossible to pull off such a 51 attack.
Satoshi Nakamoto thought that getting 51% of Bitcoin’s hash rate would be impossible because of the high costs of hardware and energy.
There hasn’t been a successful 51% attack in blockchain on Bitcoin yet, but there was a notable event that made people in the community worried. Over the course of 24 hours, the mining pool GHash.IO reached about 55% of the Bitcoin network’s total hash rate.
Even though the pool didn’t try to withhold blocks or double-spend, the event showed that it is theoretically possible for one person to get very close to the critical threshold. The public outrage that followed and the miners’ decision to leave the pool showed how committed the community is to keeping decentralization alive.
The amount of hash power that Bitcoin has and the estimated cost of the hardware and maintenance needed make a 51 percent attack very unlikely. Smaller altcoins like Bitcoin Gold (BTG) and Ethereum Classic (ETC), on the other hand, have been the victims of successful 51% attacks because their hash rates are much lower.
How Do You Detect a 51% Attack?
To detect a 51% attack, you need to keep a close eye on how the network is behaving and how the computing power is spread out. Because 51 attack events are often short-lived, it’s important to see them right away.
Key detection methods look for strange things that could mean a majority takeover or malicious chain manipulation:
- Reorganizations of chains (Reorgs): One of the main ways to find chain reorganizations is to keep an eye out for ones that happen too often or too deeply. When the network switches to a longer, competing block history, a chain reorganization happens.
- This is how a successful 51 percent attack works. The MIT Digital Currency Initiative made systems that keep an eye on these reorgs on PoW cryptocurrencies all the time.
- Hash Power Distribution: It is very important to always keep an eye on how the network’s hash rate is spread out. If you see any one mining pool or group getting close to or going over 51% control, you need to act right away.
- Double-Spent Transactions: If assets are clearly being double-spent, it means that the attacker has completed the last, evil step of the 51% attack.
- Unexpected changes in block rewards or transaction confirmations can be subtle signs of an ongoing 51 attack.
What Are the Solutions to a 51% Attack?
In a fully decentralized PoW system, it is hard to completely stop a 51% attack. Instead, the main solutions focus on making the attack too expensive and technically difficult to carry out and keep going.
Moving from the weak Proof-of-Work (PoW) system to a different consensus mechanism, like Proof-of-Stake (PoS), is seen as a good idea. To attack a PoS system, the attacker must get a majority of the network’s staked tokens. This is usually too expensive and makes it easy to find out who the attacker is.
When you delay blockchain confirmations, you make it take longer for a transaction to be final and settled. The attacker would have to keep control of 51% of the network for a longer period of time, which would make the 51 percent attack much more expensive and difficult.
In PoS or hybrid systems, setting up a penalty system is a very effective way to protect yourself. Slashing conditions are one way to punish bad actors by taking away some of their staked tokens if they break the rules of the network.
This makes it more risky for anyone who wants to attack the network. To keep user funds safe from the effects of such attacks, platforms that handle digital assets, like Jeton, often use both centralized and network-level security measures.
How to Prevent 51 Attacks in Blockchain?
Decentralization is the main defense of the blockchain, so prevention strategies focus on strengthening it. It’s harder for one person to control more than 50% of the network power if it’s spread out over a lot of people.
- Add Network Decentralization: This means making it easier for a wider range of independent miners or validators to join and lowering the barriers to entry. To avoid single-point failures, nodes should be spread out over a range of locations.
- Updates And Audits Of Protocols: Regular audits of blockchain protocols are an important part of security because they carefully look at the code to find and fix weaknesses before a 51% attack can happen. You can also make your defenses stronger by adding checkpointing systems or transaction finality mechanisms through protocol upgrades.
- Collaborative Security and Community Vigilance: An active community can help keep the network safe by working together to keep an eye on things. Sharing information about possible risks and keeping lines of communication open between participants and mining pools can help everyone respond quickly to suspicious activity.
The purpose of these preventative steps is to make sure that the cost of starting and carrying out a successful 51% attack is higher than any possible financial gain, making the attack not worth it.
Companies that handle a lot of transactions, like Jeton, are always pushing for and putting in place better security measures throughout the entire digital finance ecosystem.
Wrapping Up
The 51% attack is a basic weakness that mostly affects Proof-of-Work (PoW) systems, where a lot of computing power can be gathered. Bitcoin and other large, highly decentralized networks are almost immune to 51% attacks because they are so expensive.
Smaller altcoins, on the other hand, are at risk of being attacked repeatedly, often through hash power rental services. The attack’s main exploit, 51% double spending, makes the blockchain less secure because it lets you undo recent transactions.
Monitoring for unexpected chain reorganizations and double-spent transactions is what makes detection possible. The long-term response from the industry is to move toward consensus models that are harder to attack, like Proof-of-Stake, and to set higher security thresholds and penalty systems.
While the decentralized nature of blockchain seeks to eliminate single points of failure, a 51% attack highlights the persistent need for robust, multi-layered security in your daily finances. Whether you are navigating the risks of smaller altcoins or simply moving your money across borders, your choice of financial partner is your first line of defense.
At Jeton, we understand that while blockchain technology evolves to face threats like double-spending, you need a payment ecosystem that is already battle-tested.
Trusted by over 1 million users, Jeton provides a single account that unifies your global finances under one roof. Whether you are adding funds, exchanging currencies, or sending money to over 25 countries across Europe, we ensure every move is fast and safe.
Why the Jeton App Is Your Ultimate Financial Hub
- Total Versatility: Manage all your currencies in one app and access 50+ payment methods tailored for the European market.
- The Power of Jeton Card: Experience the ultimate convenience of contactless payments for every purchase. Need to stay on budget? Set your spending limits with a tap. Misplaced your card? Freeze and unfreeze it instantly within the app for peace of mind.
- Seamless Conversion: Move between the digital world and your daily life by converting fiat cash easily, ensuring your liquidity is never tied up.
- Safety First: Our FCA-licensed framework means your transactions aren’t just fast—they’re protected by industry-leading security standards.
Ready to simplify your global payments? Download the Jeton App via the App Store or Google Play and join a community that moves money without limits. Sign up today!
