A study from Consumer Reports indicates that 13 million Facebook users in the US alone do not use or are unaware of the social network's privacy controls.
According to the report, most Facebook users have no idea how much data they're willing giving out on the social networking site.
The study highlights Facebook users who are unknowingly giving out information by not putting their privacy settings to good use.
"Our investigation revealed some fascinating, and some disquieting trends, but ones always worth knowing for consumers who wish to keep their personal data under better control," said Consumer Reports technology editor Jeff Fox.
Consumer Reports believes many Facebook users do not fully realise just how much personal data they divulge on their Facebook page.
The report states that 4.8 million people have used the site to say where they were going on a certain day, while another 4.7 million users have "liked" health conditions or treatments, details an insurer could use against them.
These facts would not be as harmful if users limited profile access to friends and family, but according to the study many users are unaware that Facebook even has privacy settings.
The survey found that 28 per cent of Facebook users shared all, or almost all, of their wall posts with an audience wider than the people they know.
The company suggests people go the extra step to protect their personal information by making wall posts "unpublic" and exercising greater caution when posting personal information on the site.