It was the talk most anticipated at this year's inaugural Usenix Enigma security conference in San Francisco and one that even the other speakers were eager to hear.Rob Joyce, the nation's hacker-in-chief, took up the ironic task of telling a roomful of computer security professionals and academics how to keep people like him and his elite corps out of their systems.Joyce is head of the NSA's Tailored Access Operations—the government's top hacking team who are responsible for breaking into the s...