How do companies like facebook make money?

[Davis C]

MANY ASPECTS OF FACEBOOK MAKE MONEY. Social-networking Web site Facebook Inc. is quietly working on a new advertising system that would let marketers target users with ads based on the massive amounts of information people reveal on the site about themselves. . . .

The new service would let advertisers visit a Web site to choose a much wider array of characteristics for the users who should see their ads — based not only on age, gender and location, but also on details such as favorite activities and preferred music, people familiar with the matter say. Facebook would use its technology to point the ads to the selected groups of people without exposing their personal information to the advertisers.