On Monday Blizzard confirmed that Diablo 3 players found to be cheating by using hacks, bots or mods will be in breach of the EULA and will face a permanent ban from the game. This was followed up by Blizzard Community Manager Zarhym confirming that "several thousand players" have been banned as a result of this enforcement. I'm fairly certain this will have been met by those players with a great deal of wailing and nashing of teeth.
It raises the question about whether players should be banned from what is essentially perceived to be a single player game... except that Diablo 3 isn't really a single player game. Blizzard has been pushing hard for Battle.net to be akin to an integrated social network, a very poorly conceived one lacking in appropriate privacy options in my opinion. Diablo 3 has pushed this much further with the ability of people on your friend's list to randomly drop in unannounced on your game whether you like it or not (seriously, this is really irritating when you want to just do your first solo playthrough on normal or what some alone time to hac up demons). I would not be overly surprised if Heart of the Swarm pushed Battle.net even further on the Starcraft series. The issue becomes even less clear cut when you factor in that the Real Money Auction House (RMAH) is up and running on the North American servers at least; when you start throwing real money on any sort of online experience then it is necessary to clamp down on those aiming to cheat at the game and potentially wreck the AH economy. It seems fairly obvious that the mass banning and Zahrym's post is aimed at coinciding with the RMAH finally going live.
By the way, if you do plan on using the RMAH you are required to have a Blizzard Authenticator... but really there is no excuse not to have one of those already.