I think the last big hack that hit league was the no cooldown hack on summoner spells. It was pretty blatant cheating. The exploit was created through the client, the guy was able to put all 30 mastery points into the "reduce summoner spell" mastery which allowed you to spam flash across the map instantly. Its pretty hilarious and totally op hacks. Hacking on league is pretty hard, even if you make one you're assured to get banned fast.