The Infiltrator non-set comes from Saccelum Dungeon as a series of green repairable items. They drop as "Grime Covered" items and once repaired they become Infiltrators. There is no set bonus to them, they just have a common appearance and share the same name.
Decent looking pieces though not a fan of the helm. The gloves and boots are nice pieces and they come in a decent red and grey colour system so it all matches up nicely. Anyway, enjoy!