In the episode "The Adversary", Elsie Hughes follows some satellite tracking data that Bernard gave her to an abandoned theater in Sector 3. It's dark inside the theater and she has to use a flashlight. She finds an old relay transmitter beneath the floorboards of the stage. Even though the Bicameral System was abandoned decades ago, Elsie sees that someone has turned this transmitter 'on'. She discovers that Theresa was using the old bicameral control system to reprogram the Woodcutter host (to try to smuggle out Westworld data to a Delos satellite).
Elsie also finds out that someone else has been using the system for weeks to re-task several of the older hosts that have the bicameral receivers. These broadcasts have been causing serious modifications to the hosts ("changing loops, breaking loops"). She tells Bernard that some of the modifications are to the hosts' prime directives - possibly making it so that hosts could to lie to Behavior technicians and hurt humans. She can't tell who the coder is who has been making the modifications, other than it might be someone named, Arnold.
Elsie hears something as she is transferring data from the transmitter to her tablet (the newer system) for Bernard. She stops to call out both Bernard's name and "Arnold?" and look around. Then, an arm reaches out and grabs her from behind.