Multiple fail attempts in /var/log/secure

Hi AllRoot Password for LINUX system is changed. Found multiple attempts failed attempts were made on my Server and it is contentiously happening (/var/log/secure attached). My root password is changed I have limited access to system with Oracle user. Is this some Virus attack or some1 continuous making multiple attempts.

1. How can I diagnose it and rectify it? I do not have root password.
2. Currently I do not have root password how can I recover root password without restarting the server?

Thanks in advance.

Regards,
Salahuddin.