Bitcoin network is vulnerable to various categories of attacks due to the double-spending concept, which is the primary cause for most of the attacks on the network. Table 1 shows the summary of attacks on blockchain networks. Double Spending is a kind of attack which occurs when someone tries to transmit two conflicting transactions from the same address.
Moreover, research indicates that blockchain security concerns include time-jacking problems, vulnerabilities in wallet software, the “> 50%” attack, double-spending, and selfish mining tactics. Attackers provide payments to existing miners to divert from the normal execution policies.

From Table 1, it is clear that malicious users can attack a cryptocurrency in many ways. There are a significant number of attacks that can be used to exploit the vulnerabilities in the system. With the exponential rise in the popularity of cryptocurrencies, the rate of attacks on them is also extremely alarming. It can be prevented only by adequately designing the architecture of the blockchain and proper implementation of the algorithms used in cryptocurrencies.