You create a database event trigger that fires each time a user connects to the database.
For any reason, the login trigger becomes invalid. (The trigger is retrieving information from a table that may be inadvertently dropped.)
Who can connect?
Connect under a user who owns the following system privilege:
ADMINISTER DATABASE TRIGGER
SQL> connect system/manager
SQL> grant ADMINISTER DATABASE TRIGGER to scott;
SQL> connect scott/tiger
Under NT, SYSTEM cannot logon even with the ADMINISTER DATABASE TRIGGER privilege, and only a connection as “/ as SYSDBA” is possible and therefore can disable the trigger.