The Question is:
Is there a way to limit the number of times a user can simultaneously logon?
The Answer is :
Topics that discuss limiting logins to particular sources, users, and
(directly related to this question) numbers of per-user logins include
(1664), (2515), (3925), (4636), (5134), (6118), (6874), (8135).
For a partially-related discussion -- how to prevent a serial line that
receives data from initiating a login -- please review the OpenVMS FAQ
section entitled "How can I prevent a serial terminal line from initiating