How do free social networking websites make money?

[mark s]

Social networking sites earn through data exchange programs where they sell their member profiles to companies who need to conduct a survey. Like suppose if i own a music company and i wish to make a new album. I can proceed to these sites and ask them which kind of music americans like or africans like the most. They search the profiles of all their american or african members and get the results for the most popular music.

The music company pays them for this survey. Likewise many companies keep approaching these sites for thei products. And thats the only reason you are asked for your appearance, preferences etc. while creating an account with these social networking sites.

Ads and affiliate programs also contribute but thats not more than 30% of its total revenue.