http://www.reddit.com/r/Games/comments/1dglil/popular_competitive_gaming_league_esea_admins/ ESEA's TF2 6v6 league is one of the biggest TF2 leagues and the one with the highest prize pools. You have to pay for an account and then use their client to play matches with (e.g. for anti-cheat reasons). By inserting a Bitcoin miner into their client without telling anyone they used players' computers for intensive calculations to generate Bitcoins they then converted into USD. Not only does this cause the players higher energy costs for ESEA's gain but due to the way it was implemented it forced GPUs to run at max capacity for long periods of time which may have been the cause of bad performance and several reported hardware failures.