Autonomous vehicles (AVs) refer to ones that are capable of perceiving the surrounding environment and directing without human assistance. With the boom of this technology, these driverless vehicles can detect the traffic, environment and pedestrians in the street, and then they make decisions about a safe and efficient way to get to the destination. Though this technology brings advantages, the security problems of such vehicles should be taken into consideration. This paper, therefore, presents an overview of several security concerns towards vehicle-to-vehicle communication and autonomous vehicles. Moreover, this paper also provides insights into some countermeasures against cyber threats for V2V and autonomous cars.