"I suspect they have a very good idea of what he accessed on NSANet, the Agency IT system," Hayden said in an email.
After leading the NSA, Hayden went on to become principal deputy director of national intelligence in the Bush Administration and later served as director of the Central Intelligence Agency from 2006 until 2009.
Guardian reporter Glenn Greenwald, who has already published multiple stories about classified surveillance programs based on Snowden's leaks from the NSA, has suggested there are "a lot" more stories to come. According to Greenwald, Snowden gave reporters "thousands" of documents, "dozens" of which were newsworthy.
Director of National Intelligence James Clapper has described Snowden's leak as "literally gut-wrenching." In response, Greenwald tweeted: "save some melodrama and rhetoric for coming stories. You'll need it."
Barton Gellman, a Washington Post reporter who communicated with Snowden and published articles based on material he provided, wrote that the newspaper "sought the views of government officials about the potential harm to national security prior to publication" and decided not to publish some of what was provided by Snowden. Greenwald has also said his newspaper has been evaluating the materials it received from Snowden and will not be publishing it all.
Hayden also said he believed it would be possible for a computer technician like Snowden to access the volume of documents Greenwald said had been given to his newspaper. However, Hayden said he was shocked to see an employee of Snowden's rank was apparently able to access and leak materials on the NSA's top-secret surveillance programs that rely on requests made through the Foreign Intelligence Surveillance Act.
"Not surprised at the 'thousands of documents.' That's easy," Hayden wrote. "VERY surprised at which documents, eg FISA and PRISM."