What is sshguard?

Sshguard monitors servers from their logging activity. When logs convey that someone is doing a Bad Thing, sshguard reacts by blocking he/she/it for a bit. Sshguard has a touchy personality: when a naughty tyke insists disturbing your host, it reacts firmer and firmer.
Without sshguard Without sshguard bruteforce is possible.
With sshguard With sshguard bruteforce is blocked.

Sshguard supports many services out of the box, recognizes several log formats, and can operate many firewall systems. Many users appreciate its ease of use, compatibility and feature richness.

http://www.sshguard.net/