Intelligent Transportation Systems (ITS), the heart of the new revolution of smart transport, has evolved from the well-known Vehicular Ad-hoc Networks (VANETs) to become the Internet of Vehicles (IoV). In fact, the increase in the number of vehicles and the newly born technologies have stimulated the new Internet of Vehicles (IoV) or the Internet of Cars. In general, ITS aims at ensuring better traffic efficiency and reducing road accidents. However, due to different limitations and issues, these systems suffer from different security and privacy vulnerabilities. In fact, they are both vulnerable to various types of security and privacy attacks that may result in life-endangering situations. As a result, several solutions were presented to achieve the required levels of security and confidentiality. In this paper, an overview of ITS is presented stating the reasons behind the evolution from Vanet to IoV. Then, the main threats/attacks that threaten ITS are classified according to their (1) security impact and according to the (2) network layer(s) they affect. Solutions for each attack are also well presented. In addition, a security and performance evaluation and summary tables are presented to provide an overview of these surveyed solutions.