a system and method for providing a secure computing environment to untrusted computer systems is described . a carrier media and an interface are provided , the interface being connectable to a computer to enable communication between the computer and the carrier media . the carrier media encodes a secure computing environment and a boot system , upon connection of the system via the interface to a computer system and booting of the computer system , the boot system is operative to take over the boot process of the computer system and to authenticate the user , wherein upon successful authentication , the boot system is arranged to load the secure computing environment on the computer system , the secure computing environment being configured to prevent predetermined interaction from outside the secure computing environment when it is running .