An image of the site promoting Def Con 21, a large annual gathering of hackers in Las Vegas. The meeting's leader is asking federal workers to stay away from this year's event. Def Con hide caption

itoggle caption Def Con

Sean Joyce, right, deputy director of the Federal Bureau of Investigation testifies before the House Select Intelligence Committee on Tuesday. Win McNamee/Getty Images hide caption

itoggle caption Win McNamee/Getty Images

President Obama glances at Britain's Prime Minister David Cameron (right) during a news conference with European Union officials at the G-8 summit in Enniskillen, Northern Ireland, on Monday. WPA Pool/Getty Images hide caption

itoggle caption WPA Pool/Getty Images

Edward Snowden, seen during a video interview with The Guardian. Glenn Greenwald/Laura Poitras/EPA/Landov hide caption

itoggle caption Glenn Greenwald/Laura Poitras/EPA/Landov

U.S. Army Gen. Keith Alexander, commander of the U.S. Cyber Command, director of the National Security Agency (NSA), testifies during a Senate Appropriations Committee hearing on Capitol Hill, on Wednesday. Mark Wilson/Getty Images hide caption

itoggle caption Mark Wilson/Getty Images