Update README.md

added DNS NXDOMAIN Flood information

README.md

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 * Distraction Scan - this is not really a DOS attack but simply launches multiple TCP SYN scans, using hping, from a spoofed IP of your choosing (such as the IP of your worst enemy). It is designed to be an obvious scan in order to trigger any lDS/IPS the target may have and so hopefully obscure any actual scan or other action that you may be carrying out.
 
 
+* DNS NXDOMAIN Flood - this attack uses the dig utility and is designed to stress test your DNS server by sending a flood of DNS queries for non-existent domains.  When run against a recursive DNS server it tries to tie up the server and fill the cache with negative responses, slowing/preventing legitimate queries.  Works best launched from multiple attacking clients.
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 **EXTRACTION MODULES**
 
 * Send File - This module uses netcat to send data with TCP or UDP.  It can be extremely useful for extracting data.