Many users of Facebook are unaware of the privacy risks from the massive social network site or fail to take adequate precautions, a report by Consumers Reports said Thursday.
The report found nearly 13 million US Facebook users do not use, or are not aware of the site's privacy controls.
An estimated 4.8 million Americans have posted about where they planned to go on a certain day -- a potential tip-off to burglars, the report noted.
And it found that 4.7 million have "liked" a Facebook page about health conditions or treatments, details that insurers might use against them.
The report, part of the nonprofit group's State of the Net survey, estimated that seven million households using Facebook said they had trouble last year, ranging from someone using their log-in without permission to being harassed or threatened. That was up 30 percent from the previous year.
Only 37 percent of Facebook users said they have used the site's privacy tools to customize how much information is shared with third parties, according to the Consumer Reports survey.
"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," said Jeff Fox, Consumer Reports technology editor.
"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."
The report indicates Facebook gathers a considerable amount of information from users that they may not be aware of.
"Some users might be surprised to know that Facebook gets a report every time they visit a site with a 'Like' button, regardless of whether or not they click on that button, have a Facebook account, or are even logged in," the organization said.
It did give credit to Facebook for taking privacy and security "seriously" by implementing checks against abuses and inappropriate applications.
But Consumer Reports said Facebook should do more by fixing "a security lapse" that permits users to set up weak passwords including some six-letter dictionary words and to help users avoid inadvertently sharing status updates with the public.
Consumer Reports points out that all of this data collection is not without risks.
The report was based on a survey from January 16-31 of a sample of 2,002 people.
In a statement, Facebook said it works to help protect the safety and privacy of its users.
"We believe more than 900 million consumers have voluntarily decided to share and connect on Facebook because we provide them options and tools that place them in control of their information and experience," the company said.
"As part of our effort to empower and educate consumers, we always welcome constructive conversations about online privacy and safety."
The number of people using Facebook worldwide had risen to 901 million by the end of the quarter, according to company documents.
Facebook is expected to make its much-anticipated stock market debut in the coming weeks in a public offering which could raise as much as $10 billion, the largest flotation ever by an Internet company on Wall Street.