LAS VEGAS - Amid new revelations today about another expansive NSA surveillance program, agency chief Gen. Keith Alexander appeared before an audience of security professionals to defend his bulk collection of phone records and other data.

Although Alexander promised to "answer every question to the full extent possible" he took no open questions from the audience and only answered a few preselected questions that had been chosen from a survey sent to attendees of the Black Hat security conference.

Alexander was addressing surveillance programs recently disclosed by the Guardian from documents provided by NSA whistleblower Edward Snowden. Hours before he took the podium, the newspaper published a top secret PowerPoint deckdetailing the NSA's XKeystore program, which maintains a rolling archive of internet traffic vacuumed from 150 points around the world. According to the slides, NSA analysts can query the system using a broad range of selectors, from specific information like a target's email address, to category searches that might produce, for example, "all the Microsoft Excel spreadsheets containing MAC addresses coming out of Iraq."

Facing occasional hecklers from the audience, Alexander asserted that the surveillance programs have been mischaracterized by the media and others and that as a result the reputation of NSA workers has been tarnished. Extensive oversight from Congress and the courts, as well as technical protections in place – including internal auditing – prevent NSA workers from abusing their surveillance capabilities.

"What comes out is we're collecting everything. That is not true," Alexander said. He also asserted that the programs had helped thwart 54 potential terrorist plots, among them an alleged plot to bomb the New York subway system.

Alexander reiterated most of the statements the NSA has made in the past, that the programs were implemented in response to the intelligence community's failure to predict and stop the 9/11 attacks and that they're aimed at catching terrorists.

"We had intercepts of one of the 9/11 hijackers from Yemen," he said, "[but] we didn't know because we didn't have the tools and the capabilities to see that he was actually in California…. The intelligence community failed to connect those dots, and now what we're doing is putting in to the existence of these programs."

A projected screenshot showing what data NSA analysts receive from phone record databases. Photo: Courtesy Duckrabbitmedia

Two of the programs exposed by Snowden include a phone records collection program, whereby the NSA collects the call records for millions of Americans from telecoms, and a bulk collection program under the Foreign Intelligence Surveillance Act, including the PRISM program, that allows the NSA to collect internet communications for non-U.S. targets based outside the U.S.

The phone records collected under the Patriot Act, Alexander said, do not involve content of phone calls, SMS text messages, location data or subscriber information.

Instead, the NSA is provided call dates and times, the phone numbers for the callers and recipients, the duration of the call, and the source of the information (the particular telecom that provided the information). The NSA then passes select phone numbers to the FBI so the agency can use a National Security Letter to uncover the identity of the phone number's owner.

"The NSA only has the number ... FBI can take that to see where it connects to, using the NSL and the legal authorities given to them to take the next step," he said.

Data collected under the Foreign Intelligence Surveillance Act, Section 702, does involve content (emails) but targets only foreign intelligence targets. The NSA has acknowledged, however, that the communication of Americans does get scooped up in this program.

The audience of business executives and security professionals was mostly supportive of Alexander's statements. Only a couple of attendees attempted to shout him down. An audience member yelled "bullshit" at one point, while another shouted, "You lied to Congress, why do we believe you're not lying now?" Both remarks received applause from the audience.

Alexander remained composed throughout and continued with his presentation.