Traditional database with no prior security measures is becoming challenging in the era of data technology. Database storage on a central location with single point of failure and vulnerable to cyber attacks is getting exposed to big risk of being hacked with the evolution of powerful machines and modern hacking techniques. Since its commencement, the BlockChain technology has shown a promising performance for application buildup in diversed fields of life from cryptocurrency to smart contracts and decentralized applications. Although multiple studies on privacy, data confidentiality and security issues of BlockChain are performed but a systematic examination is still needs attention. In this thesis work we conduct a systematic study about the vulnerabilities of BlockChain system and review the security enhancement solutions that may point to a good future direction for further research into the area of BlockChain technology and its applications. Smart contracts are self-executable objects hosted on the 2nd generation blockchain like Ethereum, carry billions of SEK worth of cryptocoins and cannot be updated once deployed. Smart contracts are generally considered secure objects but the systematic analysis of technology and source code exposes a new class of vulnerabilities which are more likely an ethical aspect of programming than the software coding errors. Besides the literature review we empower our results with a static code analysis especially with the perspective of cyber forensics.