Players are allowed to be logged in on more than one character, depending on realm:
- Maximum 3 toons on Netherwing (TBC).
- Maximum 5 toons on Mistblade (MoP).
Multiboxing is allowed without using any kind of key broadcasting software, solely for the purposes of solo content. It is forbidden in every other situation which would require multiple players working together, unless every other player confirms that they’re in knowledge, and accepting of their co-players' intentions. In PvP environments it is forbidden without exceptions.
You can read more about rules on Stormforge realms here: