The cheat in question is called LeagueSharp and what it does is that it runs a script in the background where it lets players earn experience a lot faster than normal, spot enemies, and boosts accuracy, which obviously makes it unfair to other gamers who are trying to grind it out the good old fashioned way.
The developers are claiming that the creators of the cheat have infringed upon their copyright by reverse engineering League of Legends in order to get the cheat working. They also claimed that the makers of the cheat doxxed one of Riot’s staff members, and “disseminated personal and non-public information about a Riot employee, threatened that employee, and posted offensive comments on the employee’s social media.”
Riot is definitely not the first company to go after such developers. In the past we have seen Blizzard take on cheaters by suing bot makers and hackers, all of which should hopefully dissuade developers/hackers from creating cheats in the future, although in all likelihood we doubt this would end cheating once and for all.