Today, traffic security has become an obligation rather than a necessity. Hence to secure the traffic, provide comfort to the driver and the passengers, ensure safety of the pedestrians, infrastructure as well as the one’s sitting inside the cars, Intelligent Transport System (ITS) was created. The base of ITS is formed by a class of networks called as VANET. The VANETs make communication between vehicles and vehicle to infrastructure possible. They vary from other Ad-hoc network because of their rare characteristics. VANETs are the networks which lack centralized control and infrastructure, in which the nodes are highly mobile, topology is extremely dynamic and the links are volatile. Consequently, VANET security is threatened- the network is vulnerable to number of mischief. The easiest of all the attacks on VANETs is that on the availability – the Black-hole attack. This attack is carried out by the malicious nodes which can even be the authentic users of the network, implying that the security procedures involving encryption and authentication will not help. Therefore, to secure the VANETs against this common type of attack, we have proposed an algorithm MNP- Malicious Node Prevention. MNP improves DMV (Detection of Malicious Vehicle algorithm) as well as DMN (Detection of Malicious Nodes algorithm) in a way that MNP simply prevents the malicious nodes from participating in the packet forwarding while as both DMV & DMN first identify the malicious nodes and then remove them. This way, DMV as well as DMN cause the loss of many data packets which may be important. Hence MNP greatly improves the performance of the network when under malicious attack.