Double spending 

This is a type of attack on the blockchain network whereby a given set of coins is spent in more than one transaction; one issue that was noted here by the founder/founders of Bitcoin at the time of launch is 51 attacks. In this case, if a certain miner or group of miners takes control of more than half of the computing power of blockchain, being open in nature, anyone can be a part of the node; this triggers a 51 attack, in which, due to majority control of the network, the person can confirm a wrong transaction, leading to the same coin being spent twice.

Another way to achieve this is by having two conflicting transactions in rapid succession in the blockchain network, but if a lot of confirmations are achieved, then this can be avoided.

There are various other features that will be discussed in the coming chapters, it should be noted that all of these features exist in the present systems but considering active community support, all these limitations are being mitigated at a high rate.