Tom,

I did more research and read more documentation and this is
what I found out as a posssible solution.

I have modified the following trigger with 
AFTER LOGON BSARP.SCHEMA and compiled the trigger from
another schema who has CREATE ANY TRIGGER privilege but
does not have DBA role and it seems to be working.

I have logged on to the database using LADEV userid.
$sqlplus LADEV/LADEV

This schema has the following privileges.
SQL> SELECT * FROM SESSION_PRIVS;
     create session
     alter session
     create table
     select any table
     create view
     create sequence
     create procedure
     create trigger
     CREATE ANY TRIGGER
     execute any procedure
     administer resource manager

And I created the following trigger

SQL> CREATE OR REPLACE TRIGGER prevent_ny_users  
2  AFTER LOGON
3  ON BSARP.SCHEMA
4  DECLARE  
5     app_user   VARCHAR2(30);
6     app_region useradmin.region%TYPE;  
7  BEGIN
8     SELECT osuser INTO app_user FROM v$session
9     WHERE audsid = USERENV('sessionid'); 
10  
11     SELECT region INTO app_region 
12     FROM   bsarp.useradmin
13     WHERE  userid = app_user; 
14   
15     IF ( app_region = 'NY' ) THEN
16         RAISE_APPLICATION_ERROR(-20001,'The system is not currently 
available for this region'); 
17     END IF; 
18  END; 
19  /

Trigger created.

SQL> EXIT

Now I try to logon to the BSARP schema and PETER is the operating system user.

$whoami
PETER

$sqlplus BSARP/BSARP

SQL*Plus: Release 8.1.7.0.0 - Production on Tue Aug 20 13:49:32 2002

(c) Copyright 2000 Oracle Corporation.  All rights reserved.

ERROR:
ORA-00604: error occurred at recursive SQL level 1
ORA-20001: The system is not currently available for this region
ORA-06512: at line 13


So with this, the trigger does not have to be a DATABASE LEVEL trigger.

May I please know why you may not have suggested this. Is there any risk or serious problem involved in this method.

Thanks for your advise again.
Saradha 

All these mystifying and obscuring attempts only serve one purpose (not intended by our kind hearted folks): you created more hype than anything regarding this perceived "security issue".

Here is an easy one:

Connected to:
Oracle8i Enterprise Edition Release 8.1.7.4.0 - Production
With the Partitioning option
JServer Release 8.1.7.4.0 - Production

12:39:26 SQL> sho user
USER is "SYSTEM"
12:39:28 SQL> sho parameter o7

NAME                     TYPE          VALUE
------------------------------------ -------------------- ------------------------------
O7_DICTIONARY_ACCESSIBILITY         boolean          TRUE
12:39:33 SQL> create user lowlife identified by highlife default tablespace users temporary tablespace temp;

User created.

Elapsed: 00:00:00.00
12:40:36 SQL> grant create session, execute any procedure to lowlife;

Grant succeeded.

Elapsed: 00:00:00.00
12:40:48 SQL> conn lowlife/highlife
Connected.
12:40:59 SQL> select * from session_privs;

PRIVILEGE
----------------------------------------
CREATE SESSION
EXECUTE ANY PROCEDURE

2 rows selected.

Elapsed: 00:00:00.00
12:41:05 SQL> exec dbms_repcat_admin.grant_admin_any_schema('lowlife')

PL/SQL procedure successfully completed.

Elapsed: 00:00:01.01
12:41:30 SQL> select * from session_privs;

PRIVILEGE
----------------------------------------
CREATE SESSION
ALTER SESSION
UNLIMITED TABLESPACE
CREATE ANY TABLE
ALTER ANY TABLE
DROP ANY TABLE
COMMENT ANY TABLE
SELECT ANY TABLE
INSERT ANY TABLE
UPDATE ANY TABLE
DELETE ANY TABLE
CREATE ANY CLUSTER
ALTER ANY CLUSTER
DROP ANY CLUSTER
CREATE ANY INDEX
ALTER ANY INDEX
DROP ANY INDEX
CREATE ANY SYNONYM
DROP ANY SYNONYM
CREATE PUBLIC SYNONYM
DROP PUBLIC SYNONYM
CREATE ANY VIEW
DROP ANY VIEW
CREATE ANY SEQUENCE
ALTER ANY SEQUENCE
DROP ANY SEQUENCE
CREATE DATABASE LINK
CREATE ANY PROCEDURE
ALTER ANY PROCEDURE
DROP ANY PROCEDURE
EXECUTE ANY PROCEDURE
CREATE ANY TRIGGER
ALTER ANY TRIGGER
DROP ANY TRIGGER
CREATE ANY SNAPSHOT
ALTER ANY SNAPSHOT
DROP ANY SNAPSHOT

37 rows selected.

Elapsed: 00:00:00.00
12:41:36 SQL>