"Backstab is a technique that allows characters using a "stealther" template to maximize their damage when coming out of hiding to ambush a player victim.
For Backstab to work, the attacker has to be invisible and come out of hiding by attacking the victim with a melee weapon from behind - that is, from right behind or tilted by a 45% angle at most. If the attack is successful, its base damage is raised by 100%. Subsequent attacks don't get any additional bonus."
its not mentioned i need 100 hiding and stealth
We are going to tweak it anyway in the next patch so stay tuned!