1. A computer-implemented method comprising: receiving in a computer a request to run a live appliance by receiving in the computer a request to open a proxy for the live appliance, the proxy including a source identifier that is resolved to a location of the data source, the live appliance providing a computing environment that a user runs on the computer, the live appliance being defined by a data source that includes a version description for a current version of a virtual machine image; determining whether the computer has subscribed to the live appliance, and if not, subscribing to the live appliance on the computer, reading the data source for the live appliance, and using the current version description to initiate downloading of the current version of the virtual machine image to the computer; when the computer has subscribed to the live appliance, detecting whether a change has occurred in the data source that changes the version description designated as the current version description, and if a change has occurred, reading updated data from the data source, the updated data designating a second version description as the current version description, the second version description describing a different second version of the virtual machine image as the current version of the virtual machine image; obtaining the current version of the virtual machine image as described by the second version description; running the current version of the virtual machine image; and running a player to open the proxy, the player being an application program on the computer, the player performing the actions of creating the subscription and obtaining the current version of the virtual machine image as described by the second version description.