Facebook is the world's largest social network with nearly 500 million users around the world, up from 200 million in early 2009. Its policies, more than those of any other company, are helping to define standards for privacy in the Internet age.

The company, founded in 2004 by a Harvard sophomore, Mark Zuckerberg, began life catering first to Harvard students and then to all high school and college students. It has since evolved into a broadly popular online destination used by both teenagers and adults of all ages. In country after country, Facebook is cementing itself as the leader and often displacing other social networks, much as it outflanked MySpace in the United States.

Like other social networks, the site allows its users to create a profile page and forge online links with friends and acquaintances. It has distinguished itself from rivals, partly by imposing a spartan design ethos and limiting how users can change the appearance of their profile pages. That has cut down on visual clutter and threats like spam. In May 2007, Facebook unveiled an initiative called Facebook Platform, inviting third-party software makers to create programs for the service and to make money on advertising alongside them. The announcement stimulated the creation of hundreds of new features or "social applications" on Facebook, from games to new music and photo sharing tools, which had the effect of further turbo-charging activity on the site.

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