For some of public server that open ssh service you will got some annoy log on (/var/log/secure) that attack from ssh brute force
Jun 23 07:22:39 campus sshd[60775]: Failed password for root from 212.160.184.82 port 38212 ssh2
Jun 23 07:22:42 campus sshd[60777]: Failed password for root from 212.160.184.82 port 38626 ssh2
Jun 23 07:22:46 campus sshd[60779]: Failed password for root from 212.160.184.82 port 39056 ssh2
Jun 23 07:22:50 campus sshd[60781]: Failed password for root from 212.160.184.82 port 39348 ssh2
Jun 23 07:22:54 campus sshd[60783]: Failed password for root from 212.160.184.82 port 39621 ssh2
Jun 23 07:22:58 campus sshd[60785]: Illegal user johnny from 212.160.184.82
Jun 23 07:23:01 campus sshd[60787]: Illegal user johnny from 212.160.184.82
Jun 23 07:23:05 campus sshd[60789]: Illegal user johnny from 212.160.184.82
Jun 23 07:23:09 campus sshd[60791]: Illegal user johnny from 212.160.184.82
Jun 23 07:23:13 campus sshd[60793]: Illegal user johnny from 212.160.184.82
Jun 23 07:23:16 campus sshd[60795]: Illegal user johnny from 212.160.184.82
you can solve this problem with iptables
iptables -I INPUT -p tcp --dport 22 -i eth0 -m state --state NEW -m recent --set
iptables -I INPUT -p tcp --dport 22 -i eth0 -m state --state NEW -m recent --update --seconds 600 --hitcount 2 -j DROP
Original message from : http://chatpong.exteen.com/20050816/ssh-brute-force-iptables