Today, using an OpenGL wallhack in CS 1.6 is almost a guaranteed way to get banned. Modern iterations of VAC can easily detect modified .dll files in the game directory. Furthermore, most "Classic" servers still running today use advanced server-side plugins that detect unnatural player movement or "aim-locking" associated with these cheats.
Once the game starts in OpenGL mode, the hack is usually toggled using keys like F1 through F4 or Insert . Critical Risks cs 1.6 opengl wallhack