The Internet of Things or IoT is the vast network of physically connected devices and the technology that allow them to communicated between these devices and the cloud, as well as between the devices themselves. IoT devices also allow to transmit, receive and exchange data with other device, applications and systems like WSN and RFID. IoT devices provide a lot of facilities to human that commonly use in home, transportation, education, healthcare and business. However, due to the weak security measures this paper will review the current state of IoT security which is highlighting the vulnerabilities that expose these devices to hacking, which can be used to launch attacks on other devices or networks. For example, weak password and insecure data transfer and storage. Therefore, the preventions knowledge needs to know like using blockchain technology, security analytics, API, PKI and authentication to detect and prevent attacks.