Hidden Sniper is a heroic tier feat available to all player characters.
If a character with the Hidden Sniper feat has partial concealment against a target, he or she gains combat advantage with ranged attacks against that target.[HotFK:315]
Normally, if an attacker has total concealment from a target, the target can't see that attacker.[PH:281][RC:221] If the attacker can see the target but the target can't see the attacker, the attacker gains combat advantage against that target.[PH:279][RC:221] The Hidden Sniper feat extends the combat advantage benefit of attacks from total concealment to ranged attacks from partial concealment.