NSA director heckled by hackers at Black Hat computer security conference

General Keith Alexander makes public appearance in Las Vegas in wake of whistle-blower Edward Snowden's revelations

The director of the National Security Agency (NSA) responded calmly to heckles as he addressed an audience of hackers at the annual Black Hat computer security conference in Las Vegas.

In his toughest public appearance since the agency's electronic surveillance programmes were revealed by whistle-blower Edward Snowden, General Keith Alexander insisted the NSA's metadata collection practices ought to be a model for other countries.

Invoking 9/11, Alexander said the intelligence community had failed in the past to “connect the dots”. Now, thanks to the controversial surveillance programmes, 54 plots had been prevented worldwide, 13 in the US - including a plan to bomb the New York subway system. “The mind-set of those who work in intelligence is to save lives,” he said.

Alexander said Snowden's leak of classified data had done “serious and irreversible” damage to his agency, not least by making recruitment more difficult. Media coverage of the programmes had been overblown, he suggested. “If we listened to everyone's calls and emails, we would be held accountable,” he claimed. “What people are saying is, 'Well, they could.' The fact is, they don't.”

The NSA director doubtless came prepared for an angrier crowd than he encountered. One audience member responded to his claim that US intelligence agencies “stand for freedom” with a shout of “ Bullshit!” Another yelled that Alexander should “Read the Constitution!” He replied, to applause: “I have. You should, too.”