I am assuming you are using linux vs FreeBSD - however the suggestions for both are close to the same.
If you are running any of the following:
- RedHat v7.3, v8.0, v9.0
- RedHat Enterprise v3, v4, v5 (32/64 bit)
- CentOS v3, v4, v5 (32/64 bit)
- Fedora Core v1 to v12(32/64 bit)
- openSUSE v10, v11
- Debian v3.1, v4.0, v5.0
- Ubuntu v6.06 LTS, v8.10, v9.10, v10.04 LTS
- Mandriva 2009, 2010
- Slackware v12.2
I would suggest using a great FREE product from ConfigServer called CSF.
CSF has a great user interface if you are on a cPanel server - but will work for any of the aforementioned linux versions
there are other alternatives such as APF and BFD from R-Fx networks as well - Google the following:
APF (Advanced Policy Firewall)
BFD (Brute Force Detection)
or just visit the R-FX Network website for additional details.
There is also the method of Security by Obscurity - however that is not a FIX - but rather just hiding.
First - move your SSH Port to something other than 22.
Second - use an ssh key exchange only - and forget about passwords.
Third - only allow SSH version2
Fourth - if you have a static IP - than limit the addresses allowed to even ssh into your system via iptables and/or a firewall.
If you want some help doing any of those - please do not hesitate to ask.