The Internet of everything that is often known as The Internet of Things (IoT), is the next generation internet network that is created by intelligent objects with software and sensors, where machines can communicate with various machines and humans. The IoT industry does not have one clear set of security standards for developers and manufactures to build in consistent security. The data collected and stored with these devices such as name, age, health data, location and more can aid cyber-attack activity. The first step to face these threats is to classify it and determine the risk of attacks and threats according to different classes of layers. The present study discusses about various IoT attacks happening, classify them, its countermeasures and finding the most prominent attacks in IoT in different layers.