Are you D2, or do you just know them intimately? Read this article and file it away for future reference. The domestic political police spies of the FBI and their interface with AT&T et. al.

Meet the Spies Doing the NSA's Dirty Work.

With every fresh leak, the world learns more about the U.S. National Security Agency's massive and controversial surveillance apparatus. Lost in the commotion has been the story of the NSA's indispensable partner in its global spying operations: an obscure, clandestine unit of the Federal Bureau of Investigation that, even for a surveillance agency, keeps a low profile.

When the media and members of Congress say the NSA spies on Americans, what they really mean is that the FBI helps the NSA do it, providing a technical and legal infrastructure that permits the NSA, which by law collects foreign intelligence, to operate on U.S. soil. It's the FBI, a domestic U.S. law enforcement agency, that collects digital information from at least nine American technology companies as part of the NSA's Prism system. It was the FBI that petitioned the Foreign Intelligence Surveillance Court to order Verizon Business Network Services, one of the United States' biggest telecom carriers for corporations, to hand over the call records of millions of its customers to the NSA.

But the FBI is no mere errand boy for the United States' biggest intelligence agency. It carries out its own signals intelligence operations and is trying to collect huge amounts of email and Internet data from U.S. companies -- an operation that the NSA once conducted, was reprimanded for, and says it abandoned.

The heart of the FBI's signals intelligence activities is an obscure organization called the Data Intercept Technology Unit, or DITU (pronounced DEE-too). The handful of news articles that mentioned it prior to revelations of NSA surveillance this summer did so mostly in passing. It has barely been discussed in congressional testimony. An NSA PowerPoint presentation given to journalists by former NSA contractor Edward Snowden hints at DITU's pivotal role in the NSA's Prism system -- it appears as a nondescript box on a flowchart showing how the NSA "task[s]" information to be collected, which is then gathered and delivered by the DITU.

But interviews with current and former law enforcement officials, as well as technology industry representatives, reveal that the unit is the FBI's equivalent of the National Security Agency and the primary liaison between the spy agency and many of America's most important technology companies, including Google, Facebook, YouTube, and Apple.

The DITU is located in a sprawling compound at Marine Corps Base Quantico in Virginia, home of the FBI's training academy and the bureau's Operational Technology Division, which runs all the FBI's technical intelligence collection, processing, and reporting. Its motto: "Vigilance Through Technology." The DITU is responsible for intercepting telephone calls and emails of terrorists and foreign intelligence targets inside the United States. According to a senior Justice Department official, the NSA could not do its job without the DITU's help. The unit works closely with the "big three" U.S. telecommunications companies -- AT&T, Verizon, and Sprint -- to ensure its ability to intercept the telephone and Internet communications of its domestic targets, as well as the NSA's ability to intercept electronic communications transiting through the United States on fiber-optic cables. . .

MBV: Remember that. AT&T.

The DITU falls under the FBI's Operational Technology Division, home to agents, engineers, electronic technicians, computer forensics examiners, and analysts who "support our most significant investigations and national security operations with advanced electronic surveillance, digital forensics, technical surveillance, tactical operations, and communications capabilities," according to the FBI's website. Among its publicly disclosed capabilities are surveillance of "wireline, wireless, and data network communication technologies"; collection of digital evidence from computers, including audio files, video, and images; "counter-encryption" support to help break codes; and operation of what the FBI claims is "the largest fixed land mobile radio system in the U.S."

The Operational Technology Division also specializes in so-called black-bag jobs to install surveillance equipment, as well as computer hacking, referred to on the website as "covert entry/search capability," which is carried out under law enforcement and intelligence warrants. . .

According to former law enforcement officials and technology industry experts, the DITU is among the most secretive and sophisticated outfits at Quantico. The FBI declined Foreign Policy's request for an interview about the unit. But in a written statement, an FBI spokesperson said it "plays a key role in providing technical expertise, services, policy guidance, and support to the FBI and the intelligence community in collecting evidence and intelligence through the use of lawfully authorized electronic surveillance."

In addition to Carnivore, the DITU helped develop early FBI Internet surveillance tools with names like CoolMiner, Packeteer, and Phiple Troenix. One former law enforcement official said the DITU helped build the FBI's Magic Lantern keystroke logging system, a device that could be implanted on a computer and clandestinely record what its user typed. The system was devised to spy on criminals who had encrypted their communications. It was part of a broader surveillance program known as Cyber Knight. . .

Lately, one of the DITU's most important jobs has been to keep track of surveillance operations, particularly as part of the NSA's Prism system, to ensure that companies are producing the information that the spy agency wants and that the government has been authorized to obtain.

The NSA is the most frequent requester of the DITU's services, sources said. There is a direct fiber-optic connection between Quantico and the agency's headquarters at Fort Meade, Maryland; data can be moved there instantly. From the companies' perspective, it doesn't much matter where the information ends up, so long as the government shows up with a lawful order to get it.

"The fact that either the targets are coming from the NSA or the output goes to the NSA doesn't matter to us. We're being compelled. We're not going to do any more than we have to," said one industry representative.

But having the DITU act as a conduit provides a useful public relations benefit: Technology companies can claim -- correctly -- that they do not provide any information about their customers directly to the NSA, because they give it to the DITU, which in turn passes it to the NSA.

But in the government's response to the controversy that has erupted over government surveillance programs, FBI officials have been conspicuously absent. Robert Mueller, who stepped down as the FBI's director in September, testified before Congress about disclosed surveillance only twice, and that was in June, before many of the NSA documents that Snowden leaked had been revealed in the media. On Nov. 14, James Comey gave his first congressional testimony as the FBI's new director, and he was not asked about the FBI's involvement in surveillance operations that have been attributed to the NSA. Attorney General Eric Holder has made few public comments about surveillance. (His deputy has testified several times.)

The former law enforcement official said Holder and Mueller should have offered testimony and explained how the FBI works with the NSA. He was concerned by reports that the NSA had not been adhering to its own minimization procedures, which the Justice Department and the FBI review and vouch for when submitting requests to the Foreign Intelligence Surveillance Court.

"Where they hadn't done what was represented to the court, that's unforgivable. That's where I got sick to my stomach," the former law enforcement official said. "The government's position is, we go to the court, apply the law -- it's all approved. That makes for a good story until you find out what was approved wasn't actually what was done."