Fail2ban lee los logs (por ejemplo) /var/log/pwdfail o /var/log/apache/error_log y veta todas aquellas ips que fallan un determinado número de veces. Este veto se realiza actualizando el firewall (tipicamente iptables).

wget http://downloads.sourceforge.net/project/fail2ban/fail2ban-stable/fail2ban-0.8.4/fail2ban-0.8.4.tar.bz2?r=http%3A%2F%2Fsourceforge.net%2Fprojects%2Ffail2ban%2Ffiles%2F&ts=1286734973&use_mirror=ovh
tar -xjvf
fail2ban-0.8.4.tar.bz2
cd
fail2ban-0.8.4
python setup.py install

fail2ban-client start
fail2ban-server start

fail2ban-client start
fail2ban-server start
fail2ban-client start
fail2ban-server start

fail2ban-client start
fail2ban-server start

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