Facebook users began sharing more private data after the social network giant revamped its policies and interface, according to a study released Tuesday.
The seven-year study by Carnegie Mellon University researchers said users had been moving toward greater privacy settings from 2005 to 2009, but that the trend reversed with the Facebook changes in 2009 and 2010.
The researchers said modifications to the Facebook interface and default settings led to a significant increase in the public disclosure of personal information.
As a result, users ended up increasing their personal disclosures on the network, sometimes unknowingly, including to Facebook itself, third-party apps and advertisers.
"These findings highlight the tension between privacy choices as expressions of individual subjective preferences, and the role of the network environment in shaping those choices," said Alessandro Acquisti, one of the researchers.
"While people try to take control of their personal information, the network keeps changing, affecting their decisions and changing their privacy outcomes."
The study, appearing in The Journal of Privacy and Confidentiality, profiles data from a panel of 5,076 Facebook users and is the first study to use data from Facebook's early days in 2005.
"These findings illustrate the challenges social network users face when trying to manage online privacy, the power of social media providers to affect their disclosure and privacy behavior, and the potential limits of notice and consent mechanisms in addressing consumers' on-line privacy concerns," co-author Fred Stutzman said.
Researcher Ralph Gross said Facebook's public efforts to increase user options "may increase members' feeling of control," but that apparent confusion among some led to "increases in disclosures of sensitive information to strangers."
Facebook, which has grown to more than a billion members worldwide, has been dogged by privacy issues for years, as well as by lawsuits claiming it fails to ensure personal data is safeguarded from marketers and third-party apps.
The group agreed with a US government agency to submit to external audits of how well it guards users' data.
Complaints said Facebook had promised to honor users' privacy preferences and called on the company to stop making claims about the security of personal information -- such as age, location and friends -- that are untrue.