If you have a static IP, you can add your IP to prevent anyone else from login to SonicPanel as a root user.
- Login to your root SonicPanel
- Use Security & Firewall link from the left menu
- Set your IP
In case if your IP changes and unable to access to SonicPanel or if you need to disable restriction from the root SSH, remove the file
rm -f /usr/local/sonicpanel/allow