DenyHosts is a script designed to thwart SSH server attacks – also known as dictionary based attacks and brute force attacks.
If you’ve ever looked at your ssh log (/var/log/secure on CentOS/Redhat) you may be alarmed to see how many crackers attempted to gain access to your server. Hopefully, none of them were successful (but then again, how would you know?). Wouldn’t it be better to automatically prevent that attacker from continuing to gain entry into your system?
DenyHosts attempts to address this problem… and more.