Cyber security has emerged as a critical domain in the modern digital era due to the rapid expansion of cloud computing, artificial intelligence (AI), Internet of Things (IoT), and big data technologies. As digital transformation accelerates across industries, cyber threats have grown in sophistication, frequency, and scale. Organizations and governments face increasing risks from ransomware, phishing, identity theft, data breaches, and cyber warfare. Traditional security mechanisms are no longer sufficient, necessitating adaptive and intelligent defense frameworks. This paper explores the evolution of cyber threats, modern defense technologies such as AI-driven detection systems, blockchain security models, and Zero Trust Architecture, along with key implementation challenges. It further examines regulatory and ethical considerations in safeguarding digital assets. The study concludes that a multi-layered, proactive, and globally coordinated cyber security strategy is essential to mitigate emerging threats in the modern age.