http://us.battle.net/d3/en/forum/topic/13349455121?page=9#165
For Diablo III, multiboxing walks the strange line of being something we
technically allow, but don’t officially support.
For clarity, players are allowed to have multiple Battle.net accounts, and
each of them can have a Diablo III: Reaper of Souls license (one per
account). There is no limit to the number of Battle.net accounts a single
user can have, so long as no more than three of them have Battle.net
Balance*. There is also no restriction to how many of these accounts can be
online at once, but the methods to do so may not be supported. We do not
support third-party software, and third-party software that automates
gameplay is not allowed. Accounts found to be using third-party software that
automates gameplay risk being closed, possibly permanently.
In other words, you can have multiple accounts, and you can be online with
all of them at one time. We don’t support multiboxing in Diablo III, however,
facilitate multiboxing may violate our policies, so do so at your own risk.
* Please note that this clarification is not reflected within the EULA and
TOU at this time. We will be updating both documents in the near future to
correct this.
结论: 你敢用就用 ( ′-`)y-～