A proxy operating inside of a virtual machine that is responsible for receiving user-specified configuration information, such as credentials, and updating the configuration of the virtual machine with the user-specified values at the time of assigning the virtual machine to a user. Once the proxy updates the configuration of the virtual machine, the virtual machine is assigned the user that provided the user configuration information and the proxy can deactivate or uninstall itself from the virtual machine, such as by deleting all files, registry entries and other traces of execution.