This mass collection was exposed by the initial Snowden leak. The FISA court order published by multiple news outlets showed the government was able to engage in bulk surveillance via a single FISA request. This one targeted Verizon’s business services, but nothing about what was published suggested this was the only cell service provider responding to these blanket orders.
At the same time Snowden was airing the government’s dirty surveillance laundry, the DEA was inadvertently exposing its delicates. A particularly spectacular unforced error by the DEA saw it handing over information on its secret “Hemisphere” program in response to records requests seeking something else entirely. The information contained in this accidentally exposed presentation not only showed AT&T had employees “embedded” in the DEA to provide more instantaneous responses to phone records requests, but also that DEA agents and experts were being instructed to engage in parallel construction to hide the origin of phones records obtained with this program that were being used as evidence in court.
The DEA’s ability to obtain phone records in bulk was confirmed several months later by none other than the DEA, which released another set of Hemisphere documents to records requesters. Perhaps figuring there was no longer any reason to pretend this program didn’t exist, the DEA was more forthcoming the second time around.