Facebook Social Networking

Facebook was founded in a Harvard University dorm room less than four years ago. Now No. 2 in social networking sites, it has become the tech debutante of the year -- the hottest company inside the hottest Internet trend. Facebook allows thousands of programmers to add features that help its users update one another on their every move and thought.

Microsoft Corp. on Wednesday won the right to invest in Facebook Inc. Microsoft is betting that online social networking is the marketing platform of the future, letting advertisers narrowly target their brands to people who group themselves around such affinities as the Lakers or French cooking.

Facebook, which employs fewer than 400 people, is the sixth-most-visited site on the Web, according to research firm ComScore Networks. The majority of its users are now overseas.