Mark Zuckerberg (center), Facebook founder, chairman and CEO, applauds at the opening bell of the Nasdaq stock market on May 18, 2012, from Facebook headquarters in Menlo Park, Calif. (Associated Press/Nasdaq via Facebook, Zef Nikolla)

Photo by: Zef Nikolla

Mark Zuckerberg (center), Facebook founder, chairman and CEO, applauds at the opening bell of the Nasdaq stock market on May 18, 2012, from Facebook headquarters in Menlo Park, Calif. (Associated Press/Nasdaq via Facebook, Zef Nikolla)