IoT is an acronym for Internet of Things. It is the revolutionary area that transforms the digital world into a device world. IoT helps in not only fulfilling human requirements, but also they act as a communication medium between humans and electronic devices. The birth of IoT started in early 2000s, but since then, it is an amazing fact that now at least 65% of devices are connected with IoT technology with the term “smart” in their prefix and it would be up by 30% at the end of 2016 (Gartner Survey, 2015). Since then, many security issues were raised, and have been risen all these years due to the flaws in that devices. This made attackers to take advantage over that devices and started controlling them. This chapter studies IoT application layer protocols, services offered and gives an idea of existing cyber attacks and threat. In addition, the authors give the possible attacks on the IoT devices, in particular at application layer, and give the necessary precautions to overcome the cyber attacks both for consumers and vendors.