This paper provides a comprehensive survey of IoT security, focusing on application areas, security threats, and solution architectures. The authors highlight the critical need for high security in IoT applications, which are increasingly prevalent in various sectors such as smart cities, smart environments, smart metering, and smart agriculture. They discuss the unique security challenges faced by IoT, including data privacy, authentication, and management issues. The paper also reviews existing security solutions, emphasizing four major approaches: blockchain, fog computing, machine learning, and edge computing. Each approach is detailed, with specific examples and benefits highlighted. The authors conclude by identifying open issues and future research directions in IoT security, emphasizing the need for rigorous penetration testing and the integration of AI-based techniques to enhance IoT security.This paper provides a comprehensive survey of IoT security, focusing on application areas, security threats, and solution architectures. The authors highlight the critical need for high security in IoT applications, which are increasingly prevalent in various sectors such as smart cities, smart environments, smart metering, and smart agriculture. They discuss the unique security challenges faced by IoT, including data privacy, authentication, and management issues. The paper also reviews existing security solutions, emphasizing four major approaches: blockchain, fog computing, machine learning, and edge computing. Each approach is detailed, with specific examples and benefits highlighted. The authors conclude by identifying open issues and future research directions in IoT security, emphasizing the need for rigorous penetration testing and the integration of AI-based techniques to enhance IoT security.