DNScat: "DNScat (pronounced 'D-N-S cat') is a 'swiss-army knife' tool to tunnel traffic through DNS servers. It provides a bi-directional communication through DNS servers, and in conjunction with PPP, can be used to set up a virtual private network (VPN).

DNScat, like a swiss army knife can be used for a variety of purposes, including:

* penetration testing of networks behind firewalls
* sending messages though firewalled networks
* setting up a VPN though firewalled networks
* learning how to detect covert channels through DNS servers
* and more...