What is double spending?

While the Blockchain successfully solves the problem of double spending by using cryptography and a majority consensus to verify if a transaction is valid, there remains some vulnerability to the system in the form of a 51% attack. For instance, if someone was able to control the majority, or 51%, of the network they would essentially have the power to commit double spending and all sorts of malicious activity and get away with it.

However, for a single person or group to control more than half the mining power of an entire network is no easy task, especially for a humungous network like Bitcoin’s. The bigger the network in size, the stronger the protection against attacks and data corruption. Thus, a 51% attack on Bitcoin or other large cryptocurrencies is extremely unlikely due to the size and mining power (aka hash rate) of the network. Once a Blockchain becomes sufficiently established, the chances of a single group or person having enough computing power to launch a 51% attack becomes very low.

Additionally, changing the previously confirmed blocks gets more difficult as the chain grows, because the blocks are all linked and cryptographically hashed to the previous block, forming one long chain & history of transactions. In order to alter a single transaction or block successfully you would have to alter all the blocks in the chain which is virtually impossible. For this reason, the Bitcoin network has never been successfully hacked.