VMS Help SET, SECURITY, Qualifiers, /CONFIRM  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Controls whether SET SECURITY prompts for verification before
    performing the operation. Valid responses are YES, NO, TRUE, and
    FALSE. Answers are not case sensitive and can be abbreviated to
    one letter. To stop processing the command at any point, type
    QUIT or press Ctrl/Z. To cancel the verification procedure but to
    proceed with the command, type ALL.