The head of the U.S. National Security Agency defended the government's much-criticized surveillance program against hecklers among a crowd of computer systems analysts Wednesday, but also had a challenge for them: If you don't like it, lend your talent to build a better one. 

"You're the greatest tech talent anywhere in the world. Help us," Army Gen. Keith Alexander said at the hacker conference for the buttoned-up corporate and government security analyst crowd, not the one later in the week for the more counter-culture types.