In the annals of intelligence, no word is more associated with secret government intelligence reports, especially those produced for policy-makers based on raw intelligence. UFO reports in the 1950s. The most brittle reporting on Soviet leadership intentions. Intercepted phone calls between Chinese and Pakistani nuclear officials.
Way back when — at least since middle of the 1950s — the intelligence community used the UMBRA code word to inform the reader of a certain report that the original source for the intelligence was of the most sensitive category. At the NSA, back then, there were three levels of source sensitivity. UMBRA was the five-letter code word used for Category III sources. (Other words: MORAY and SPOKE).
If a document was stamped TOP SECRET UMBRA at the top and the bottom, you'd know that the agency went to great lengths to obtain the embedded information.
The NSA today uses "ECIs" — Exceptionally Controlled Information compartments — to protect the fragile methods it uses to obtain sensitive information from "UMBRA"-quality sources. Let's say that the NSA tapped into the communications hub of a country using an access point at Company A's Bermuda facility. Suppose that particular access picked up the president of that country discussing plans to help Iran circumvent treaties. The NSA would protect the location at which the intercept occurred by an ECI — the "how we got this" — and designate the sensitivity of the source by using UMBRA.
In the reports themselves, the NSA might refer to "clandestine sources" or "special intelligence" — without naming the exact source and certainly not the mechanism by which the source was intercepted. UMBRA reports are fairly widely distributed.
More narrowly distributed reports would be given an additional designation: "GAMMA." These reports would describe, in narrative form, or even with excerpts, actual conversations or dialog intercepted directly by the NSA or a partner in such a manner that the reader would know that the NSA has direct access to the communication.
Technically, the association of "UMBRA" with "Category III" SIGINT remains classified, though that secret was long ago broken. The association of the word with the NSA itself is not.
It's been a long time since anyone without a clearance has seen a document marked UMBRA. In 1999, the term was supposedly "eliminated" from the lexicon of classification markings.
The Washington Post's story about the NSA's intercepted communications include a reference to a target package prepared by the agency before the Special Operations Command captured Muhammad Tahir Shazad, an al Qaeda heavyweight, in 2011.
The classification line reads as follows:
TOP SECRET // COMINT // UMBRA // ORCON / REL USA, FVEY
UMBRA, in this context, might be used differently than the UMBRA of old. The double slash indicates that it is not a SIGINT or COMINT marking and has its own meaning. Since the target package was prepared for policy-makers and policy-implementers, though, the word might have some meaning associated with the war on terrorism.