AFAICT, they haven't told anybody exactly where they get the data about you that you don't give them. Presumably, they buy it from one of the commercial persona

AFAICT, they haven't told anybody exactly where they get the data about you that you don't give them. Presumably, they buy it from one of the commercial personal information brokers that maintain dossiers on consumers and sell that info. Or they might enter into information-trading arrangements; I don't know. The article only says that they 'harvest' information about you from external non-facebook sources and then add that to the secret internal profile that they maintain about you.