The armor itself can be found on the corpse of an assassin inside a secret room in Hag's End. While Hag's End can be entered before accepting the quest, the pull chain to open the secret door will not appear until after Olava has been visited.
Wearing this piece of armor grants the following bonuses:
- Backstab – The backstab effect doubles the amount of sneak attack damage done with one-handed weapons. In addition, wearing the full Ancient Shrouded Armor set grants a 25-point armor bonus. It cannot be disenchanted.
This means the gloves cannot be improved past flawless quality without boosting the Smithing skill over 100. This can be achieved by wearing enchanted apparel and/or using potions to fortify Smithing.