SN Defense, also known as Tier Defense, is a shellcode created by ydccdy on May 23, 2015.
This code was primarily executed using DBOF, partly because it was the only method available at the time to run shellcodes as SuperNulls.
Initially, the file was named 81.st and was first utilized by Ice-Oro-Mizuchi. A year later, the authors Volcrz and K_NaCa implemented it in their character R'lyeh Text Special. From that point onward, many other cheap creators adopted it in their own characters, making the file one of the most copied and reused in the community.
Although this technique is referred to as SN Defense or Tier Defense, it is not a defensive mechanism. This is because the shellcode nullifies game exploits, effectively rendering characters nonfunctional. Over time, various iterations of this technique have been developed. Some of these simply nullify DBOF, which was used to counter dsrugal back in the day. Later updates introduced additional features, such as nullifying %f, DBOF, and more.
1.0/1.1[]
As already stated in the StateDef Overflow article, this exploit is no longer effective in newer engine versions, as any StateDef header with a longer size than 255 bytes will be truncated.