Top US security agency turns to hackers for help

The largest-ever hacker gathering in Las Vegas proved to be a perfect recruiting opportunity for the head of the US National Security Agency.

Keith Alexander, a four-star general and director of the US National Security Agency, took the stage in a black T-shirt and jeans on Friday to address the country's largest hacker convention, Defcon.

He delivered a recruiting pitch to the thousands in attendance, including hackers, professional defenders and researchers.