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Harvard sophomore Mark Zuckerberg creates a web site called Facemash in his dorm room and shares the link around campus. Zuckerberg hacked the Harvard student database to populate the site with pictures and make a “hot or not” game, in which users compared photos of students. That game was eventually shut down.

Zuckerberg and co-founders Dustin Moskovitz, Chris Hughes and Eduardo Saverin launch Facebook for Harvard students. A month later it opens to students of Yale, Columbia and Stanford. Facebook would soon become a phenomenon across college campuses in America.

Facebook ends the year with “more than 30,000” people working on safety on the platform, according to Zuckerberg, and a commitment to invest “billions of dollars” in security annually.