Facebook is one of the largest websites in the world, with more than 500 million monthly users. The site was started in 2004 by founder and CEO Mark Zuckerberg when he was an undergraduate student at Harvard.
Since September 2006, anyone over the age of 13 with a valid e-mail address can join Facebook. Users can add "friends" and send them messages, post announcements, and update their personal profiles to notify friends about themselves.
The name of the service stems from the colloquial name for the book given to students at the start of the academic year by university administrations in the US. The intention of the book is to help students to get to know each other better.
Facebook was founded by Mark Zuckerberg with his college roommates and fellow computer science students Eduardo Saverin, Dustin Moskovitz and Chris Hughes. The website's membership was initially limited by the founders to Harvard students, but was expanded to other colleges in the Boston area, the Ivy League, and Stanford University. It gradually added support for students at various other universities before opening to high school students, and, finally, to anyone aged 13 and over.
Facebook has met with some controversy. It has been blocked intermittently in several countries including Pakistan, Syria, the People's Republic of China, Vietnam, Iran, Uzbekistan, Saudi Arabia, and Bangladesh. It has also been banned at many places of work to discourage employees from wasting time using the service.Facebook's privacy has also been an issue, and the safety of their user accounts has been compromised several times. Facebook has settled a lawsuit regarding claims over source code and intellectual property.
A January 2009, a Compete.com study ranked Facebook as the most used social network by worldwide monthly active users, followed by MySpace. Entertainment Weekly put it on its end-of-the-decade "best-of" list, saying, "How on earth did we stalk our exes, remember our co-workers' birthdays, bug our friends, and play a rousing game of Scrabulous before Facebook?" Quantcast estimates Facebook has 135.1 million monthly unique U.S. visitors.