UPDATE:
Vitiate telepathically dominated (all) inhabitants of Imperial World (i.e. Ziost):
The Emperor escaped destruction on Yavin 4, and now his presence has been felt on the planet Ziost, once powerful throne world of the Sith Empire. You are called upon again to face this galactic menace when your allies realize that the entire planet's inhabitants have been mind-controlled. And while the Emperor’s ultimate plan is still unknown, you do know he must be stopped.
Source: http://www.swtor.com/blog/welcome-game-update-3.2-rise-emperor
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As the Sith Emperor gradually dominates the free will of everyone on Ziost, both Lana Beniko, Minister of the newly formed Sith Intelligence, and Theron Shan, a spy for the Galactic Republic, are trying to stop the chaos. Your leadership in guiding them through the conflict on Ziost is critical to uncovering the former Sith Emperor's terrifying plan.
Source: http://www.swtor.com/gameupdates/rise-of-the-emperor
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More information:
"The scores of dead have nourished me. I am awakened. And I bring with me--death!" – Sith Emperor
Obsessed with achieving immortality, the Sith Emperor has targeted his own former subjects on the planet Ziost, with every death seemingly extending his dark power. Speaking through those he's possessed, he controls powerful pawns like Master Surro, the leader of a team of elite militarized Jedi known as the Sixth Line.
Source: http://www.swtor.com/gameupdates/rise-of-the-emperor