Sister's Account Hacked (he's on right now)

I'm on right now, and my sister's death knight is on. They haven't played in months, and this character, Kephas (Bonechewer horde) is in Storm Peaks, at level 73, and will not answer me. He set his status to DnD. I texted my sister, and she is not on (but did play SC2 last night). I appreciate your help.

PS, the only way I knew the character was online is it's in my guild. I've already removed bank access (but not kicked from the guild).