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A thumbs up 'Like' icon is on the door at the entrance to Building 10 at Facebook headquarters in Menlo Park, California, May 15, 2012. Facebook, the word's most popular social networking website, expects to raise USD 12.1 billion in what will be Silicon Valley's largest-ever initial public offering (IPO) later this week. AFP PHOTO / ROBYN BECK (Photo credit should read ROBYN BECK/AFP/Getty Images)

A thumbs up 'Like' icon is on the door at the entrance to Building 10 at Facebook headquarters in Menlo Park, California, May 15, 2012. Facebook, the word's most popular social networking website, expects to raise USD 12.1 billion in what will be Silicon Valley's largest-ever initial public offering (IPO) later this week.   AFP PHOTO / ROBYN BECK        (Photo credit should read ROBYN BECK/AFP/Getty Images)