HP OpenVMS Guide to System Security: OpenVMS Version 8.4 > Chapter 14 Using Protected Subsystems
A protected subsystem is an application that, when run, causes the process running the application to be granted one or more identifiers. For as long as a user runs the subsystem, the user's process rights list carries these additional identifiers. “How Protected Subsystems Differ from Normal Access Control” shows how a protected subsystem adds a second level of access control to traditional controls.
Possession of subsystem identifiers is limited to the period users are executing the application. Once the users exit from the application, the identifiers are removed from their process rights lists. Subsystem identifiers are also removed from the rights list whenever users enter a Ctrl/Y sequence or attempt to create a subprocess with the DCL command SPAWN. (In this respect, use of the subsystem identifiers is identical to the operation of images installed with privileges.)