Utility to help sys admins thwart SSH crackers

 DenyHosts is a program that automatically blocks SSH
 brute-force attacks by adding entries to /etc/hosts.deny.
 It will also inform Linux administrators about offending
 hosts, attacked users and suspicious logins.
 .
 Synchronization with a central server is possible too.
 .
 Differently from other software that do same work, denyhosts
 doesn't need support for packet filtering or any other kind
 of firewall in your kernel.
 .
 DenyHosts unfortunately does not support IPv6.