DenyHosts is a set of Python scripts that will help automate the process of blacklisting IP addresses that are hammering your SSH service. So obviously you know that I’m talking about something related to *NIX systems here.
It does this by appending offending IP addresses into your
hosts.deny file. In addition to that, it has some cool features such as keeping logs of all banning actions, purging of old entries, and emailing the administrator of any newly blacklisted host. You can get the full list of features from the DenyHosts features page.