That's exactly the scenario I found at Test-IQ.com, a quiz advertised on Facebook. The site's home page makes no mention of a fee--you'd have to click to the privacy policy and read to the bottom to discover the $7 charge. Other sites, such as IQ-Test-Results.com, slip in recurring monthly fees for registered users.

Then there are quizzes like CheckMyPersonality.com. Its Web site says, "Happy! (Shy) Sad? Outgoing, Fun? Which are you? Find Out for Free with CheckMyPersonality.com." This site goes as far as to periodically access your credit card once you've signed up. I discovered a line in the company's privacy terms that gives it an ongoing right to "verify that your credit card account is valid and has credit available" by charging fees and later crediting them off.

Worse, that line isn't even in the terms linked on the home page--it's in a secondary set buried deeper in the site. It comes up under a link labeled "Privacy Policy" on the fourth screen you reach as you fill out the quiz. The page is hosted on a different domain, and is separated from the site's privacy policy page, but it is still branded as CheckMyPersonality.com.

CheckMyPersonality.com also authorizes its owners to dig up all kinds of information on you. The company states that it may use "third-party service providers" to track down everything from your household income to your buying habits--and then resell that data to marketing agencies.

"These [types of sites] are data-mining havens where users willingly opt-in from the very beginning," says Ryan Jacobson, an attorney and cochair of the Entertainment Media and Privacy Law Group at the law firm SmithAmundsen in Chicago. "I'm afraid that the average user fails to recognize or take the time to understand what privacy rights he or she is actually giving up by responding."

CheckMyPersonality.com, incidentally, didn't respond to our requests for comment.

The Trust Factor

Ultimately, deciding whether you should take an online quiz comes down to a question of trust: Are you comfortable putting your information--personal or financial--into the owner's hands? Remember, even if you don't directly input data, it can be passed along. Such is the case with Facebook, where just opening an application automatically grants its developer access to your entire profile. And don't assume that the developer isn't going to use the information within.

"The very intimate and detailed nature of the information featured on Facebook profiles makes such a database very valuable to marketers," says Guillaume Lovet, a senior manager with security company Fortinet.