When former NSA contractor Edward Snowden, shown here on a banner in Hong Kong, leaked details of government surveillance programs to the press, it ignited a firestorm of controversy and made many people start thinking seriously about their online data.

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Current events may have you worrying about the NSA spying on you. But how about acquaintances or even non-governmental strangers on the Web? If you've been using the Internet for any length of time, there's probably lots of information floating around out there about you, from your and your friends' social networking accounts, messages boards, blogs and other sites you've registered for and then forgotten. In fact, even if you're some rare creature who has never even perused the Web (and if so, we're confused about how you're reading this article), there's likely still far more information about you online than you would have believed possible, and even the most alarmingly personal details can be had for free or for a price.

Privacy violation isn't just for people with public profiles on social sites or the fillers-out of a gazillion online sweepstakes and surveys. We are all becoming increasingly aware that Web sites are tracking us with cookies so that they can target advertisements at us, among other things. But to a large extent, that information is anonymous and not searchable by Joe Blow, even though it might be connected over multiple affiliated sites that may know who you are. There are, however, companies that dredge up all sorts of information about you, under the guise of white pages or people finders or background checkers or market research services, and then make your information available online.

On these data collection sites, anyone can type in your name, e-mail, phone number or other identifying information (sometimes even your Social Security number) and find things like your date of birth, home address, previous residences, your home's valuation, the names of your relatives, your religion, your ethnicity, hobbies, places of employment, sites where you have accounts and a host of other scary details. Some provide links to things like your social networking profiles or your Amazon wish list. Many of these data brokers will display a good bit of information for free, and for a one-time, monthly or annual fee will provide lots of other information, including legal and criminal records.

Anyone -- including friends, enemies, prospective employers, law enforcement and lawyers investigating cases -- can find a host of information about you on these Web sites, some of it accurate and some not so accurate.

The simplest way to find out what's out there about you is to do searches for your name, e-mail addresses and other identifying information. You can start with a search engine such as Google, but you are likely to get an overwhelming amount of information unconnected to you -- or people who share your name or screenname. A search engine can be useful to see the top hits that your contact information yields, just to check on your online reputation. But searching the data collection sites will likely prove far more fruitful -- and perhaps frightening.