<p><span style="font-weight: 400;">When you pay cash for a product or service, the paid cash cannot be used by you again for any other transaction. This is a fact as far as physical currency is concerned, which can usually be spent only once. But in the absence of proper measures, the digital currency can be spent again. A fraudster may use one of the ways to disrupt the system or reverse a transaction after it&rsquo;s confirmed and processed. They make it look like the currency was never used. Then the same currency may be used again. This is known as double-spending.</span></p>
<p><span style="font-weight: 400;">Blockchain helps prevent double-spending. Each transaction is registered on a blockchain and waits to be mined. Once a transaction is mined, its validity is stored in the blockchain and broadcasted on the network. This ensures that once a transaction is confirmed, it cannot be reversed or duplicated.</span></p>
<p><span style="font-weight: 400;">There can be a possibility that a person makes the same cryptocurrency transaction to two different people. However, the transaction which gets mined first will be confirmed and the other one is removed from the network. Now, you may be wondering if both the transactions can be mined at the same time. It&rsquo;s possible that both are confirmed simultaneously but the one which gets more blocks (more miners mine the transaction) stays in the network and the other one is removed.&nbsp;&nbsp;&nbsp;</span></p>
<p><span style="font-weight: 400;">A blockchain usually prevents double-spending but if there&rsquo;s a 51% attack then it may be possible. The attack refers to a condition in which an organisation or person has mining computational power that is over 51% of the total network&rsquo;s computational power. In such a scenario, the organisation or person can compromise a transaction and double spend. </span> <span style="font-weight: 400;">&nbsp;</span></p>