Double spending occurs when an attempt is made to send the same Bitcoin twice from one wallet to another, usually with malicious intent.

Normally, nodes verify that the Bitcoin in the wallet is available to be spent by cross-checking all previous transactions. Miners then process these transactions on the blockchain. This proof-of-work mechanism is defined by the Bitcoin protocol and is designed to prevent Bitcoin from being spent twice.

However, a double-spend attack is not impossible because if a malicious attacker is able to acquire more than 51% of the hash rate, then he can manipulate the blockchain and send himself more Bitcoin, especially if the transactions do not are not yet confirmed. .

The likelihood of a double-spend attack occurring is relatively low because the amount of money needed to purchase enough nodes, ASIC miners, and subsequent infrastructure to execute a 51% attack would not make it worthwhile, given the number of people checking the blockchain today.