Third parties can see your data. Many Facebook apps garner data about users' friends. That means even if you don't use a particular app it could have access to your data just by way of one of your friends who is using it.

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U.S. privacy laws are lax. Good luck getting your hands on the full bevy of information social networks have on you, at least if you live in the United States. That's because online privacy laws in the U.S. are generally weaker than those in other places.

Problems are escalating. Eleven percent of respondents, or a projected 7 million households, said in 2011 they had experienced a problem with Facebook such as being harassed or someone else logging into their accounts without permission. That's up 30 percent from last year.

The Consumer Reports findings agree with other studies recently conducted. For example, , even after reading privacy policies most users of Facebook and Google still don't understand how the websites handle their information and how other Web users can discover it.