Users understood the privacy policies less well than they did government documents or bank card agreements, the study said. They earned comprehension scores between 35 and 40 out of 100 for both policies. The survey asked just over 400 people to read the companies' policies and then answer questions about them online.

"We forced users to pay attention to this, but even through forcing them to pay attention, they still couldn’t understand what was in these privacy policies and were failing to grasp the basic information that was supposed to be communicated," said Brian Rafferty [cq], global director of insight at Siegel+Gale.

The study is hardly the first to find that users are uneasy with how much of their information becomes public through their use of websites and mobile applications. It is among a growing body of research demonstrating the ineffectiveness of privacy policy statements as a way to keep users informed about how their data is used.

After reading the policies, just 23 percent understood that their Google+ profile is visible to anyone online. Just 30 percent knew that even with the strictest privacy settings activated, their Facebook user names remain public.

The study also pointed to problems with Google's efforts earlier this year to notify users that it was consolidating the privacy policies for its diverse services. Less than half of users understood that the company's privacy policy related to their use of YouTube and Google Maps.