This chapter investigates the convergence of big data technologies and cybersecurity, emphasizing how data-driven approaches are reshaping threat detection, analysis, and defense mechanisms in cyberspace. It begins with a foundational overview of network structures, key principles of cybersecurity confrontation, and the theoretical underpinnings of information security. The chapter then categorizes major sources of big data in cyberspace, including user-generated data, industry-specific information, traffic logs, online public opinion, and publicly available datasets commonly used in security research. Core big data-driven security applications are examined, such as event correlation analysis, anomaly detection, content security assessment, and situational awareness modeling. The chapter further explores prevailing cybersecurity threats targeting big data systems and reviews mainstream defense technologies, including real-time monitoring, access control, and encrypted storage. Finally, real-world case studies from leading Internet companies are presented to demonstrate the design and deployment of large-scale big data security infrastructures. Through this exploration, the chapter underscores the strategic role of big data analytics in enhancing cyber defense capabilities and addressing the evolving security challenges of the digital era.