Diablo III Multiboxing Officially Allowed

Blizzard clarifies the rules regarding running multiple characters at once

The process of running multiple Diablo III characters at one time is called multiboxing, and has always operated in a grey area according to Blizzard's rules. A recent discussion about multiboxing brought some useful clarification from the a Blizzard Community Manager, to specify exactly what sort of behavior is and isn't allowed. It's a tricky subject, because it can quickly fall into issues of setting up macros or other functions that do multiple actions with one keypress, which very clearly is not allowed.

To run multiple characters at once requires owning multiple copies of Diablo III, so this is something that the vast majority of players will never try. There are programs (only a Google search away) that help automate the process, for the people interested in running multiple characters together. These programs let one keyboard and mouse send their commands to multiple Diablo III clients at once, routing commands from a player to multiple clients. That activity is what the European Community Manager Vaneras discussed, editing his posts multiple times to try to make it exactly clear what is and isn't allowed.
This is a very tricky topic to address, because there are quite a few different approaches to multiboxing out there and only some of them goes against our Terms of Use.

It is an issue if and when multiboxing automates gameplay, but as long as the player who is multiboxing is the legitimate account holder on all the involved accounts, and as long as all the characters being played are 100% under the player's control without any kind of automation involved, then we are okay with it.

Edit: Removing the air plane analogy, because looking at it in retrospect, I can see that it wasn't really very accurate. Please look to my next response for further clarification: http://eu.battle.net/d3/en/forum/topic/5825582768?page=2#25
Again, the question of whether or not multiboxing is permitted is a very hard one to address.

You are free to play more than one character at the same time using more than one client at the same time, but each character must be played the same way you would play a single character normally in a single client. This means that one character must not react and perform actions automatically based on actions performed by another character. You can send commands and instructions to multiple characters at once, which is fine of course, as long as each action performed by each character is a result of direct player interaction and player choice.

Multiboxing characters must be controlled 100% by the player!

Edit: Edited the post for clarification purposes.
As is clearly stated, this does not allow people to use macros, where one button press can generate multiple actions (whether for one character, or many characters). While it's a fine distinction, it's one that Blizzard has decided upon, to control what is allowed within the game.
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