NEW YORK (CNNMoney) -- As Facebook barrels toward its IPO, one of its biggest lightening-rod issues -- privacy -- is drawing a fresh spotlight. A Consumer Reports study released this week estimates that 13 million American Facebook users have never set or simply don't know about the site's privacy controls.
While some people overshare, others are taking steps to camouflage themselves. A quarter of those Consumer Reports surveyed said they falsified information in their profiles to protect their identity -- up from 10% two years ago.
Consumer Reports based its conclusions on a survey of 2,000 U.S. households. It estimates Facebook's entire U.S. user base at around 150 million people.
"Our investigation revealed some fascinating, and some disquieting trends," Consumer Reports Technology Editor Jeff Fox said."Facebook really is changing the way the world socially communicates and has become a successful service in part by leveraging copious amounts of personal data that can be spread far wider than its users might realize."
The report honed in on some of Facebook's trickier privacy settings, including its controversial policy of sharing some of each user's data with third-party apps used by their friends.
"Unless an individual has chosen their privacy settings meticulously, one of their friends who runs an app could grant it access to their information without their knowledge, including information that was set to 'friends' only view," the report notes.
Facebook did not immediately respond to a request for comment on Consumer Reports' study.
Only 37% of those Consumer Reports polled say they've used Facebook's privacy tools to control what kind of information various apps can collect.
In September, Facebook rolled out real time apps that allow users to broadcast their actions, like what music they're playing and what online articles they're reading. That data stream is a treasure trove for marketers and advertisers.
Consumer Reports' study comes as Facebook is preparing for its IPO -- an offering in which the company plans to raise as much as $13 billion by selling shares to the public. Facebook updated its IPO filing on Thursday and set a preliminary price range for its shares of $28 to $35 each, which would value the company at up to $75 billion. 
