In a new study, Barracuda Labs analyzed a random sampling of more than 70,000 fake Twitter accounts that are being used to sell fake Twitter followers.

via The underground economy of social networks.

This underground economy consists of dealers who create and sell the use of thousands of fake social accounts, and Abusers who buy follows or likes from these fake accounts to boost their perceived popularity, sell advertising based on their now large social audience or conduct other malicious activity.