Run SQL Developer and connect to your Oracle Database as SYSDBA.
Check to see whether auditing is enabled and an audit trail is being written to a database table by executing the following command in SQL Developer:
show parameter audit_trail
If auditing is not enabled, run the following command in SQL Developer:
alter system set audit_trail="DB" ;
Then restart your database.
To record unsuccessful logons, run the following command in SQL Developer:
audit session whenever not successful;
After you execute this command, all failed logon attempts will be directed to the database audit trail (the SYS.AUD$ table).
To find failed logon attempts, execute the following script in SQL Developer: