The logo and a page of mobile app "Snapchat" are displayed on tablets. Hackers broke into Snapchat, the popular mobile app, accessing the phone numbers and usernames of 4.6 million users and publishing them online. Lionel Bonaventure/AFP/Getty Images hide caption

itoggle caption Lionel Bonaventure/AFP/Getty Images

Twitter made its debut on the New York Stock Exchange in November. Both the social media giant and the relative newcomer Snapchat are valued in the billions, but neither company has yet turned a profit. Emmanuel Dunand/AFP/Getty Images hide caption

itoggle caption Emmanuel Dunand/AFP/Getty Images