Tired of the abuse I'm getting on one of the servers exposed to the Internet, I've installed APF, the Advanced Policy Firewall, and BFD, Brute Force Detection on the machine. Webhostgear.com has easy-to-follow installation instructions for APF and BFD respectively.
While plain vanilla iptables was enough to protect the machine from most routine attacks, incessant attempts at logging in to a couple of well-known services on well-known ports was filling the logs and consuming an extrodinary amount of the bandwidth. Now, a script kiddie attempting 13,000 logins will find the machine no longer responding on that IP address.
Interesting technology. BFD uses a script run as a timed job to parse logs, pick up repeats, and bans them by scriping a command line and submitting it to APF. APF also uses the excellent DShield.org list of known problemmatic machines and networks. Very cool. While BFD comes with a set of scripts to parse common exploits, it didn't have one for my ftp server. I'm not sure I've grokked what's needed to set up my own script of rules, but as I couldn't find one on Google, I'll give it a shot, and share my results back to the community once I've got it working.