Anders can venture with Hawke into the Grey Warden prison in Vimmark Mountains. Since Anders is a Warden, he starts hearing the voice of Corypheus through the taint. As the voice is getting louder, Anders struggles to shut him out. Finally, Justice takes him over, turns hostile to Hawke and summons two shades. Once Justice is defeated and the shades are killed, Anders apologizes and promises to try harder to hold against the voice and Justice."
Oh, one more thing. You might want to warn people not to take Anders into the DLC. I can't remember what exactly happens, but I seem to recall Justice freaking out and having to fight him at the end. My Rogue ended up having Anders as the only Mage I always had in the party, so I remember that fight sucking. cost me a ton of healing potions.