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 deck detailing 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.”