With more than one billion users, popular social networking site Facebook is celebrating its ninth birthday today (Monday).

The social networking site was launched on Feb 4, 2004. It is owned and operated by Facebook, Inc.

Facebook was started in 2004 by Mark Zuckerberg (one of the five co-founders of the networking site). As of September 2012, Facebook has over one billion active users.

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 eventually to anyone aged 13 and over.

The social networking site made its public listing in May last year.