Step1

Run SQL Developer and connect to your Oracle Database as SYSDBA.

Step 2

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

Step 3

If auditing is not enabled, run the following command in SQL Developer:
alter system set audit_trail="DB" ;
Then restart your database.

Step 4

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).

Setp 5

To find failed logon attempts, execute the following script in SQL Developer:
select
os_username,
username,
terminal,
to_char(timestamp,'MM-DD-YYYY HH24:MI:SS')
from
dba_audit_trail;