The mystery surrounding how much domestic spying the US government has been conducting on its own citizens will only intensify in the coming days, as a growing number of the nine major internet companies linked to an alleged top-secret data-mining program deny they had anything to do with it.

The stories in the Guardian and Washington Post contend that the National Security Agency and FBI were jacking directly into the central servers of the companies and scooping up all sorts of personal data in a hunt for terrorist activity. Publicly, these agencies insist that they only do that overseas, to foreigners, while the tech firms concerned insist they aren’t involved and have never heard of such a scheme.

That may or may not be true, and finding out the gritty details is sure to become the next parlor game in Washington. One thing is for sure, though. If PRISM is what the two newspapers say it is, it is the biggest domestic spying program that the United States has ever conducted, and by orders of magnitude.

“It looks from what I’ve seen to be larger than anything I thought we were doing,” says Paul Rosenzweig, author of a recent book, Cyber Warfare.

Rosenzweig should know. As a former acting assistant secretary at the Department of Homeland Security, he was one of those people given the kind of Top Secret / Sensitive Compartmented Information clearances needed to work on any project as sensitive as this. But, he says, “I wasn’t read in on this.” (He wouldn’t comment on what he was “read in on”).

The reports about PRISM come a day after The Guardian reported on another data mining program that allowed the US government access to metadata about every single phone call flowing through the trunk lines at Verizon, one of the country’s biggest wireless carriers. The Wall Street Journal has since reported (paywall) that secret court orders also enable such surveillance at AT&T and Sprint, the other two big carriers, and that the orders are renewed every three months; NBC says it has been happening on every call in the US for the last seven years.

James Bamford, author of three books on the NSA, says the disclosures have certainly raised a lot of questions about what’s going on out at the agency’s headquarters in Fort Meade, Maryland. But Bamford says the two programs have may solved another mystery that he’s been wrestling with for a year now—why the NSA needed to build such a cavernous and secret complex way out in Bluffdale, Utah. “They need that data center to store all of this stuff,” Bamford told Quartz.

Bamford said that he and other security experts familiar with the NSA have long snickered about how the NSA’s spooks and engineers were vacuuming up their emails and everything else they were doing. “It used to be a joke,” he said. “Now, it’s not a joke at all.”