Okay, you don't want "grey area", nor have you used addons, yet you want to multibox? What are you worried about, sensitive data being stolen? If you're so worried about the data, DON'T USE THAT COMPUTER FOR NON-SECURE STUFF. The fact you want to multibox (a grey area with players, it's tolerated by blizzard) is hilarious. Get your priorities straight, then use your head.
You don't want to use software because of a 'gray area' - use the grey matter between your ears and then MAKE A DECISION AS TO WHETHER OR NOT IT IS OKAY. Follow the general rule: one action = one keypress per character.
Think it out some more. Software is the most economical way to do it.
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