1. A method of processing data using a memory having a plurality of memory regions, a given memory region within said plurality of memory regions having an associated owning process having rights to control access to said given memory region, said method comprising:receiving a request to initialise a guest execution environment at a security controller other than said guest execution environment or a hypervisor for managing the guest execution environment;
claiming with the security controller one or more regions of memory which are allocated as being for use by the guest execution environment, but which are initially claimed to be owned by said security controller so that the security controller is the associated owning process for said one or more regions;
storing with said security controller executable program code of said guest execution environment within said one or more regions of memory claimed and owned by said security controller; and
after storing the executable program code of said guest execution environment within said one or more regions, transferring with said security controller ownership of said one or more regions from said security controller to said guest execution environment, so that the guest execution environment becomes the associated owning process for the one or more regions.