Mastering computer security requires more than just technical knowledge of software, systems and networks?it demands analytical thinking, a problem-solving mindset, and creative reasoning. These skills are best cultivated through practical challenges and structured problem-solving.  This book presents a collection of questions and problems on a wide range of topics typically taught in introductory computer security courses, including basic concepts and principles, authentication techniques, access control models and methods, network security, software vulnerabilities, and malware. Topics and features: The exercises range in complexity to ensure progressive skill development?from foundational knowledge (e.g., defining and understanding basic security ideas and principles) to more advanced problem-solving (e.g., applying knowledge to analyze a security protocol, synthesizing concepts, making judgments about a design, or creating solutions). Each exercise is accompanied by a solution intended to serve as a learning aid and facilitate self-assessment. Some solutions include historical notes and additional references that could be useful to readers who are willing to explore a subject in more depth. The problems include practical scenarios and real-world cases, ensuring that readers understand how principles are applied in practice. The content is organized into sections and chapters that are mostly self-contained, so readers can explore them in any order. The material is flexible and can be adapted for various courses and audiences, allowing instructors and learners to select topics based on their needs. This unique textbook/reference offers broad appeal:  The exercises are intended to complement other learning materials and are tailored to different skill levels, allowing beginners to build a strong foundation while offering advanced challenges to more experienced learners.