Vehicular Ad hoc Networks (VANETs) are
emerging mobile ad hoc network technologies incorporating
mobile routing protocols for inter-vehicle data communications
to support intelligent transportation systems. Among others
security and privacy are major research concerns in VANETs
due to the frequent vehicles movement, time critical response
and hybrid architecture of VANETs that make them different
than other Ad hoc networks. Thus, designing security
mechanisms to authenticate and validate transmitted message
among vehicles and remove adversaries from the network are
significantly important in VANETs. This paper presents
several existing security attacks and approaches to defend
against them, and discusses possible future security attacks
with critical analysis and future research possibilities.