The proper way to address this error:

Your backup folder MIGHT be visible to the public

To correct this issue, move the .htaccess file from wp-content/plugins/wp-dbmanager to /home/wordp/public_html/wp-content/backup-db

…IS
1. uninstall the backup plugin through it’s menu (shown in attached screen shot)
2. follow instructions when you click Uninstall WP-DBmanager
3. Goto plugins
4. Deactivate WP-DBmanager if it is not yet deactivated
5. Activate WP-DBmanager.