Defending the security of interconnected systems is shifting to depend upon methods for determining the level of trust to be placed in devices and users, with mandatory enforcement of access control policies and robust mechanisms for ensuring the integrity of communication between mutually-authenticated entities. Virtualization-based security leverages trust in the hypervisor to provide strong mechanisms to virtual machines, enabling increased protection, in server, client and embedded deployments. The interfaces provided by the hypervisor for inter-domain communication determine critical properties for data isolation and control of information flow. Hypervisor-Mediated data eXchange describes key aspects of these data transfer primitives and has some support in Hyper-V. The first Open Source implementation of HMX is Argo, a Xen hypervisor feature developed with the OpenXT Project.