Oracle - BLOQUEAR TOAD

hola..

tengo oracle 8i server..
necesito desactivar o negar la entrada a los usuario
que utilizar conexiones ODBC Y QUERY BUILDER, TOASD

como hago

TENGO ESTO.. PERO ME BLOQUEA TODO

CREATE OR REPLACE TRIGGER block_tools_from_prod
AFTER LOGON ON DATABASE
DECLARE
v_prog sys.v_$session.program%TYPE;
BEGIN
SELECT program INTO v_prog
FROM sys.v_$session
WHERE audsid = USERENV('SESSIONID')
AND audsid != 0 -- Don't Check SYS Connections
AND rownum = 1; -- Parallel processes will have the same AUDSID's

IF UPPER(v_prog) LIKE '%TOAD%' OR UPPER(v_prog) LIKE '%T.O.A.D%' OR -- Toad
UPPER(v_prog) LIKE '%SQLNAV%' OR -- SQL Navigator
UPPER(v_prog) LIKE '%PLSQLDEV%' OR -- PLSQL Developer
UPPER(v_prog) LIKE '%BUSOBJ%' OR -- Business Objects
UPPER(v_prog) LIKE '%EXCEL%' -- MS-Excel plug-in
THEN
RAISE_APPLICATION_ERROR(-20000, 'Development tools are not allowed on PROD DB!');
END IF;
END;
/
SHOW ERRORS