I guess mines was back when I used to do reverse engineering. It was when I was able to patch VRay rendering system for 3dstudio max. At the time vray had all nasty checks that would rendering artifacts randomly. Once you thing it was patch correctly it would mutate on you and produce watermarks or just a black screen.Not to mention if not patch correctly the person information that leaked it could of been recovered. For me this was a pretty big accomplishment when I was around 15-16, fun times.