So ... have a security suggestion for you ...
change the sshd (daemon on server) port from standard 22 to a high port - pick one from 49152–65535. Something like 49200?
Before doing that ask yourself if you have an alt way of getting to server. Got Webmin installed? Check into that ... open sourced cPanel.
Within one minute of a new server being brought up on internet it usually has it's first poke and probe on port 22.
My 2 cents, of course.
'SoS', Ken