The NSA is tracking cell phone movements, generating 5 billion records a day

Documents leaked by former NSA contractor Edward Snowden show that the National Security Agency is gathering a massive amount of data about the location of millions of cell phones all over the world. The news, which contradicts the agency’s claims that it had only experimented with tracking but then abandoned the efforts, is likely to fuel the ongoing scandal over the U.S. government’s surveillance of phone and internet activity.

According to the documents, reported on Wednesday by the Washington Post, the NSA has been harvesting the location of cell phones by using interception equipment plugged into key nodes of phone carriers’ networks. As the Post explains, the system relies on U.S. companies to collect the information at cell towers and other relevant locations to obtain nearly 5 billion records a day about cell phone whereabouts:

the sigad relies on two unnamed corporate partners described only as ARTIFICE and WOLFPOINT. According to an NSA site inventory, the companies administer the NSA’s “physical systems,” or interception equipment, and “NSA asks nicely for tasking/updates.”

For privacy advocates, the new revelations could prove especially troubling since cell phone location patterns can be deeply revealing and, unlike voice or internet data, it’s not possible to disguise movements through encryption or private networks. As an ACLU technologist told the Post (which has graphics of how the system works), the only practical recourse to avoid the collection is to unplug from the networks and “live in a cave.”

While the use of disposable burner phones could theoretically provide a way to evade detection, the documents suggest that the activation of a burner phone triggers a “special scrutiny” response with the NSA (security experts have previously speculated this practice was underway.)

Like the voice calls collected from Verizon(s vz) and the data collected from tech companies under the program known as PRISM, the NSA is storing the location records as metadata, and not keeping records about every specific individuals. Only in specific instances, it appears, does the agency hone in on certain people. The sheer volume of metadata, however, is apparently taxing the NSA’s ability to store it: one sources says there are already 27 terabytes, or more than double the text content of the Library of Congress’s print collection. (The CIA is also struggling under too much data, as its chief technology officer told Gigaom at StructureData).

The distinction between metadata and individual tracking is not likely to comfort privacy advocates, however, since the legal process for obtaining specific data is conducted by a secret court that won’t share its decisions that explain why the process is legal under the Constitution.