Internet of Things (IoT) is growing exponentially in multifolds and going to offer opportunities in various fields such as business, education, medical, healthcare, transportation, industry, environment, smart homes, smart cities and many more. Without human intervention, the smart devices of the IoT system will be able to sense, collect and transfer data over internet. It has various issues on security, due to use of multiple smart devices, networks and software those are vulnerable and prone to hack. The paper mainly emphasizes on IoT applications, attack surface and security vulnerabilities, technological and security challenges with protective measures with future directions of IoT.