Facebook is a free social networking website founded in 2004 by Mark Zuckerberg and his Harvard colleagues. It allows users to connect with friends, share photos and messages, and join groups. Though originally only for Harvard students, it expanded to other schools and is now open worldwide. Facebook's growth has been rapid, reaching over 1 billion active users by 2012. It makes most of its revenue from advertising and has had a highly successful public offering. While Facebook remains the largest social network globally, it faces competition from other regional social platforms.