A device for securely controlling communications among or within computers, computer systems, or computer networks, comprising: (a) a primary access port to which an "owner" computer program, computer, computer system, or computer network is connectable to access shared computer resources; (b) a secondary access port to which a non-owner computer program, computer, computer system, or computer network is connectable to access the shared computer resources; (c) a transfer port to which a shared computer resource is connectable to provide controlled access to that computer resource from computer programs, computers, computer systems, or computer networks connected to the access ports; and (d) a separate physical communication path to and from each access port and each transfer port, where access permissions and restrictions for each communication path are set by the owner of the device through the primary access port.