Ah yes, a tale as old as time—or at least as old as old-school MMO players. You've got multiple World Of Warcraft accounts, for one reason or another, and are "multiboxing" to sign in to both accounts simultaneously. Blizzard have updated their policy on multiboxing to clarify that multiple instances of the game are fine, but they'll be issuing warnings and bans to players using third-party software to automate playing them.
"We will soon begin issuing warnings to all players who are detected using input broadcasting software to mirror commands to multiple accounts at the same time (often used for multi-boxing). With these warnings, we intend to notify players that they should not use this software while playing World of Warcraft. Soon thereafter, the warnings will escalate to account actions, which can include suspension and, if necessary, permanent closure of the player's World of Warcraft account(s)."
Blizzard say that they have examined the use of third-party software for broadcasting multiple inputs and determined that it has had an increasingly negative effect on the game. Being able to simultaneously control multiple accounts at once, rather than just having them both running, can be used to create bots that automate in-game tasks. Among other things, it can be a real detriment to in-game economies when a fleet of characters can be sent out to collect resources.