Within MyPHRMachines, we distinguish between the Execution and Storage layers. Each Virtual Machine (VM) in the execution layer represents the virtualization of specific application software (or a software bundle) serving the purpose of either viewing or analyzing patients’ health data. Patients can log into MyPHRMachines and decide which VM to load in a given session using a standard Web portal. The Hypervisor is a generic piece of software to start, stop, clone VMs, and control their Internet access. For our prototype, we decided to use VirtualBox, an off-the-shelf hypervisor. Being heavily used in several industries, VirtualBox benefits from periodic functionality updates and security reviews. Note that, as discussed more in depth later, the VMs for specialist software are stateless and deprived of Internet access.