There are many programs that help you secure your servers. There are simple firewalling programs and there are complex network intrusion detection systems. Depending on your demands, there seems to be a solution for everyone. Unless you’re picky and you think you can do better – like I did, when I wrote my own combination of syslog-ng and Linux iptables, skipping the middle man.
August 2013 update. There seems to be a problem using the syslog-ng file() destination on /proc in Linux. See http://valentijn.sessink.nl/?p=458 for more information.