Links and resources ...

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Hprobe Packet Generator
http://sourceforge.net/projects/hprobe/
This handy tool differs from other packet generators because of it's built-in packet sniffer. When using a traditional packet shaping tool, one generally has to either code it's own receiver or use a third-party packet sniffer like tcpdump.

Nessus 3.0.1 is out!
http://www.nessus.org/
The third major release of the excellent open source vulnerability scanner is here. New features include smarter resource consumption and faster scanning. Nessus and it's parent company, Tenable Security, have recently received mixed feedback from the open source community in response to their switch from a LGPL license to a proprietary licensing model.

Portknocking for the true paranoid
http://cryptknock.sourceforge.net/
Portknocking is an interesting technique where one or multiple ports remain closed until a particular sequence of packets is sent to the target host. The packets are sniffed by the portknocking daemon which opens the hidden port(s) for a short time window. Now there's nothing wrong with Portknocking, it serves it's purpose extremely well if you want to access a stealth box from the network. Unless you're extremely paranoid.

Cryptknock is a suite of tools that allows the truly schizophreniac to use encrypted portknocking, reducing the chances of having "them" eavesdrop on your secret handshakes. Who said overkill was bad.