Agency veterans described the tactic as an infrequent but important security measure, a means of protecting vital secrets by inserting fake communications into routine cable traffic while using separate channels to convey accurate information to cleared recipients.

But others cited a significant potential for abuse. Beyond the internal distrust implied by the practice, officials said there is no clear mechanism for labeling eyewash cables or distinguishing them from legitimate records being examined by the CIA's inspector general, turned over to Congress or declassified for historians.

Senate investigators uncovered apparent cases of eyewashing as part of a multi-year probe of the CIA's interrogation program, according to officials who said that the Senate Intelligence Committee found glaring inconsistencies in CIA communications about classified operations, including drone strikes.