StarCraft. Overseas, Blizzard's RTS is played professionally and broadcast on national television. And, like most sports leagues, the competitions have drawn a following from the illegal gambling market.
The growing controversy surrounds a number of professional gamers, including some famous and top-ranked players, accused of intentionally throwing matches to exploit the illegal gambling operations. The Korean police are currently investigating the accusations. However, considering the underground nature of the scandal, it's clear that it will take a long time before all potential suspects are apprehended.
For further coverage, Team Liquid offers a recently updated and extensive overview of the scandal.