—Virtualization refers to the abstraction between the hardware resources and the software running on a system, making it possible to run multiple operating systems on one physical machine, each one completely separated from the other. It has both technological as well as economical roots, and its adoption is still being driven accordingly, in a race to balance between these two aspects in order to get the most out of it. Enough is being said about the efficiency and the cost savings of this technology, but very little about the security implications it might bring. Many of the security issues in virtualization arise due to the difficulty of inspecting and monitoring a virtual machine continuously, as well as the quality and usefulness of the information that can be monitored and extracted. This monitoring can be achieved by virtual machine introspection (VMI) which is leveraged from hypervisor (VMM-virtual machine monitor). Balancing between security and efficiency cannot be achieved using Network-Based IDS or Host-Based IDS but by VMI. Keywords— Virtual machine(VM), Virtual machine introspection(VMI), Intrusion detection System(IDS), hypervisor security, cloud security, virtual machine monitor(VMM)