-----------------------------------------
답변자가 기본적으로 참고할 내용입니다.
- 배포판(옵션)    : 
- 커널버전(옵션)
  : 
- 데몬버전(예:apache
 1.3.27) : 
- 데몬설치유형(RPM/컴파일/기타)
 : 
-----------------------------------------
/var/log/messages입니다.

 1 15:54:15 ns opensshd[22303]: Illegal user operator from 218.38.14.121
May  1 15:54:15 ns opensshd[22303]: Failed password for illegal user operator from
218.38.14.121 port 52147 ssh2
May  1 15:54:15 ns opensshd[22305]: Illegal user adm from 218.38.14.121
May  1 15:54:15 ns opensshd[22305]: Failed password for illegal user adm from
218.38.14.121 port 52153 ssh2
May  1 15:54:16 ns opensshd[22307]: Illegal user apache from 218.38.14.121
May  1 15:54:16 ns opensshd[22307]: Failed password for illegal user apache from
218.38.14.121 port 52166 ssh2
May  1 15:54:16 ns opensshd[22309]: Illegal user irc from 218.38.14.121
May  1 15:54:16 ns opensshd[22309]: Failed password for illegal user irc from
218.38.14.121 port 52172 ssh2
May  1 15:54:16 ns opensshd[22311]: Illegal user irc from 218.38.14.121
May  1 15:54:16 ns opensshd[22311]: Failed password for illegal user irc from
218.38.14.121 port 52180 ssh2
May  1 15:54:16 ns opensshd[22313]: Illegal user adm from 218.38.14.121
May  1 15:54:16 ns opensshd[22313]: Failed password for illegal user adm from
218.38.14.121 port 52190 ssh2
May  1 15:54:16 ns opensshd[22315]: Failed password for root from 218.38.14.121 port
52197 ssh2
May  1 15:54:16 ns opensshd[22317]: Failed password for root from 218.38.14.121 port
52204 ssh2
May  1 15:54:16 ns opensshd[22319]: Failed password for root from 218.38.14.121 port
52212 ssh2
May  1 15:54:17 ns opensshd[22321]: Illegal user jane from 218.38.14.121
May  1 15:54:17 ns opensshd[22321]: Failed password for illegal user jane from
218.38.14.121 port 52220 ssh2
May  1 15:54:17 ns opensshd[22323]: Illegal user pamela from 218.38.14.121
May  1 15:54:17 ns opensshd[22323]: Failed password for illegal user pamela from
218.38.14.121 port 52226 ssh2
May  1 15:54:17 ns opensshd[22325]: Failed password for root from 218.38.14.121 port
52232 ssh2
May  1 15:54:17 ns opensshd[22327]: Failed password for root from 218.38.14.121 port
52238 ssh2
May  1 15:54:17 ns opensshd[22329]: Failed password for root from 218.38.14.121 port
52243 ssh2

보시면 포트를 바꿔가면서
SSH2 에 접속하려고 시도하는 듯 싶습니다.

이사용자 접근 못하게 할 수 있는 방법이 없을까요?