This item is provided when you start the quest  The Path of the Righteous which starts with Baristolth of the Shifting Sands at Cenarion Hold in Silithus.
A character can also receive this item when they are deputized by another character using the [Proxy of Nozdormu].
When you have the Agent in your bag, it allows you to loot [Silithid Carapace Fragment] from the corpses of silithids in Hive'Ashi, Hive'Regal, and Hive'Zora. When you turn 200 Fragments into Baristolth, you earn Brood of Nozdormu reputation.
Patches and hotfixes
Patch 1.9.0 (03-Jan-2006): Added