Hackers will be in the audience when the head of the U.S. National Security Agency makes a scheduled speech before an annual conference at a Las Vegas Strip resort.

Army Gen. Keith Alexander has been unapologetic in recent public appearances about the methods the NSA uses to, in his words, connect the dots and go after bad guys who aim to kill people.

But he'll face a skeptical and tech-savvy audience in his keynote comments Wednesday at the annual Black Hat conference at Caesars Palace.

Alexander acknowledges the ongoing debate about federal intelligence agencies collecting telephone and Internet information.

But he says the issue is stopping terrorist attacks.

He has insisted that it's "flat not true" the spy agency is listening to people's phone calls and reading their emails.