ippersonality is a linux kernel patch for the 2.4.x tree that allows the user to fool os-fingerprinting techniques. It works with iptables by adding targets for the packets to be be parsed and and sent back to its origin. It uses configuration files in netfilter scripting format that contain information describing the "habits" of various operating systems making os-fingerprinting applications like nmap believe your linux system runs the operating system you specified. Since the targets by default handle only packets specific to most port-scanning (though this can be changed), it does not weaken the strength of your TCP/IP stack. Ippersonality can be found at http://ippersonality.sourceforge.net.