a9lh is the nickname given to arm9loaderhax, which abuses a weakpoint in the arm9 function of the 3ds systemA9lh Is the nickname given to ARM9 Which is the main componet necessary to achieve total control over the system to allow any user modification to be done. That is considered the main security of the system that prevents use of installing custom unauthroized cia and other stuff that nintendo doesn't want people to have cause it would allow anyone to do whatever they can within system limitations. I think