Hidden service routing works quite differently that regular exiting traffic. Twice the number of relays are involved, and the traffic is end-to-end encrypted in

Hidden service routing works quite differently that regular exiting traffic. Twice the number of relays are involved, and the traffic is end-to-end encrypted instead of being visible to any relay (such as an exit node). Correlation attacks are always possible to a global passive adversary (which NSA may or may not be), but as far as I can tell, they seem much harder to pull off against hidden services.