Abstract: This paper, employing the rigorous PRISMA framework for literature review, thoroughly examines the intricate nexus between cryptocurrencies and illicit activities, focusing on Bitcoin, Ethereum, Monero, and other altcoins. The PRISMA framework ensures a systematic and comprehensive synthesis of scholarly articles, reports, and case studies, enhancing the credibility and reliability of the findings. The paper uncovers Bitcoin's pivotal role in past illicit activities, shedding light on vulnerabilities, and delves into Ethereum's misuse for smart contract-based illegal activities, Monero's privacy-centric role, and potential risks associated with altcoins like Zcash and Litecoin. Additionally, a comparative analysis of these cryptocurrencies is presented regarding their involvement in illegal activities. The study emphasizes the ongoing need for research to combat evolving criminal strategies and technological advancements in the crypto landscape. Acknowledging the challenges in regulating digital assets effectively, the research underscores the necessity for comprehensive regulatory frameworks. Despite complexities, the paper provides a nuanced perspective on cryptocurrencies' roles in illicit transactions, advocating for regulatory measures and technological solutions. By utilizing the PRISMA framework, the research enhances the reliability and methodological rigor of its literature review, contributing valuable insights for policymakers, researchers, and industry stakeholders grappling with the complexities of regulating the crypto space. Keywords: Cryptocurrency, Illicit Transactions, Bitcoins, Money Laundering, Altcoins