http://www.reddit.com/r/Games/comments/1dglil/popular_competitive_gaming_league_esea_admins/
ESEA Member unisolsz discovered that the client required to play on ESEA was running a bitcoin miner. After players were complaining about virus alerts being set off from the client and unusually high GPU usage and BSOD errors.
The thread he made regarding this can be found here
ESEA admin, lpkane admits that it was an "April Fools joke" that was mistakenly left in the client that ran for only 2 days. He claims only 2 bitcoins were mined in total (Roughly around $280 USD) and that it would go towards a prize pool. Source
He later corrects that it was running for 2+ weeks and actually raised 29~ bitcoins (around $3,602.21 USD) and to apologize awarded all current ESEA premium members a free month of service and that all the money raised will go into the prize pool. He also claims that all bitcoin mining code was removed from the client. Source #2
Bitcoin miners use up 100% of GPU processes and lead to a lowered hardware lifespan, and can actually damage it permanently.