Social media giant Facebook Inc. may know more about you than you think after a recent report claimed that the company was acquiring information about users from third-party information brokers.

Pro Publica claims that Facebook has been acquiring “detailed dossiers” obtained from commercial data brokers about users’ offline lives to better refine what ads they show those users in their Facebook feeds. Perhaps making the issue more explosive is that Facebook, despite promising to be transparent about the data it collects on individual users, doesn’t disclose the information it has gained through third parties. Facebook justifies the lack of disclosure on third-party data “because it’s widely available and was not collected by Facebook.”

“Our approach to controls for third-party categories is somewhat different than our approach for Facebook-specific categories,” Facebook Privacy and Public Policy Manager Steve Satterfield said. “This is because the data providers we work with generally make their categories available across many different ad platforms, not just on Facebook.”

Satterfield said that users should contact third-party information brokers if they did not want it made available and that the details of who the company buys data from are available from a Facebook help page. Facebook currently works with six companies to collect information including financial data and credit score information on users: Transunion, WPP, Oracle, Experian, Epsilon and Acxiom.

Despite being able to contact companies to opt out of their data services, doing so is said to be anything but easy. Many companies require that personal details, such as drivers licenses, be revealed to do so, with a number said by Pro Publica to require the request be sent in writing via traditional mail.

Since all this is mostly legal, the broader question comes down to privacy in the Internet age, not just the legal implications of big companies gathering information.

Image credit: Tom Murphy/Wikimedia Commons/ CC 3.0