Blockchain is often seen as highly secure due to its unchangeable, decentralized nature, making it appealing for use in legal and medical applications. However, this perception is only partially accurate. In recent years, Blockchain and cryptocurrency systems have experienced significant breaches, with an estimated $3.8 billion lost to hacks in 2022 alone. As more businesses adopt Blockchain, securing these systems becomes critical. This chapter overviews current attack methods targeting Blockchain ecosystems and vulnerabilities specific to smart contracts. It outlines strategies for mitigating these risks, such as improving network security and implementing better contract auditing. Additionally, the chapter reviews several notable Blockchain attacks that resulted in significant financial losses, analyzing the methods used and how similar attacks can be prevented in the future. By exploring the vulnerabilities and potential solutions, this chapter aims to contribute to the ongoing efforts to strengthen Blockchain security in real-world applications.