Cloud security is becoming bombilate word in IT industry area associated with security measure and concealment. In this paper we outline the security measure of virtual machines in virtualized cloud environment. Since virtualization is key component of cloud computing. Notably, attackers can discover exposure of cloud system and compromise VMs for launching Distributed-Denial of Service (DDoS) attacks. Among the cloud service models such as PaaS, SaaS and IaaS, Specially in IaaS (Infra-structure as a Service) the detection of attack is enormously unmanageable. Since many cloud employers install exposure diligences on their VMs. To overcome such limitation we proposed NIDSV, which is designed based on Alert Correlation Graph & Countermeasures. NIDSV undertake to resolve this limitation by using AODV routing protocol depending on routing mechanism and few node fixed as Intrusion Detection System (IDS) to determine exposure virtual machines. The entire NIDSV system is imitate by utilizing Network Simulator-2 (ns2) and examine the execution using simulation parameters. Simulation result shows performance of NIDSV in the form of average delay, delivery of data packet and throughput.