This morning my fail2ban log shows the following 80 times in a period of 3 seconds... 2009-06-03 07:50:07,700 fail2ban.filter : WARNING Unable to find a corresponding IP address for host156-192-110-95.serverdedicati.aruba.it Yesterday I showed 80 lines from the same source over a period of 17 minutes. Also 125 lines from the following over a period of 5 seconds. 2009-06-02 08:03:36,528 fail2ban.filter : WARNING Unable to find a corresponding IP address for c906091a.spo.static.virtua.com.br Yesterday I tracked the error to repeated attempts to hack into pure-ftp via a dictionary type brute force method. I disabled pure-ftpd-mysql then as I'm not using ftp. I do show in the logs that fail2ban is banning other attackers in the expected way. But apparently someone is able to hide their ip in a way that fail2ban can't ban them. Anyone know a way to fix this?