Blizzard has shut down over 50,000 Battle.net accounts for cheating. It also suspended over 8,000 CD keys and permanently banned over 3,000 CD keys.
Cheating is no fun for gamers, so it's obviously bad for business. It's also an area of potential liability for gaming companies who are easier to sue than the cheaters.
Coverage at http://www.shorl.com/hyjastegrifuha