LinuxQuestions.org - How to stop things like these

I just got a mail from my system ,when I opened this I find something unusual that worried me,so can any one help me regarding this..

showing some part of the message..
today

Code:

--------------------- pam_unix Begin ------------------------



 sshd:

    Authentication Failures:

      root (211.75.183.115): 7 Time(s)

      unknown (59.49.14.12): 2 Time(s)

      root (office.meijob.com): 1 Time(s)

    Invalid Users:

      Unknown Account: 2 Time(s)

and yesterday

Code:

--------------------- SSHD Begin ------------------------





 Failed logins from:

    211.75.183.115 (211-75-183-115.HINET-IP.hinet.net): 7 times

    211.99.138.146 (office.meijob.com): 1 time



 Illegal users from:

    59.49.14.12: 2 times





 Received disconnect:

    11: Bye Bye : 7 Time(s)



 **Unmatched Entries**

 reverse mapping checking getaddrinfo for 211-75-183-115.hinet-ip.hinet.net failed - POSSIBLE BREAK-IN ATTEMPT! : 7 time(s)

 pam_succeed_if(sshd:auth): error retrieving information about user sales : 1 time(s)

 pam_succeed_if(sshd:auth): error retrieving information about user staff : 1 time(s)



 ---------------------- SSHD End -------------------------

And how will I stop thing like these ,how to handle thos Illiegal users,Invalid accounts,Unknown accounts.. etc...