Whitepaper entitled ‘NIDS Polymorphic Evasion – The End?’. This paper explains how even the most modern of NIDS fail to detect polymorphic shellcode.
You can download it from the following link: https://packetstormsecurity.com/files/download/39008/ecl-poly.txt
Source: https://packetstormsecurity.com/files/39008/ecl-poly.txt.html