fail2ban: new module.

Fail2ban scans log files (e.g. /var/log/apache/error_log) and bans IPs
that show the malicious signs -- too many password failures, seeking for
exploits, etc. Generally Fail2Ban is then used to update firewall rules
to reject the IP addresses for a specified amount of time, although any
arbitrary other action (e.g. sending an email) could also be configured.