Thanks to sites such as Facebook and Wikipedia you can find out your friend's favourite colour and even your celebrity crushes' birthdate.

However, just how much information about you could your friends, or a potential employer for that matter, find out? And could it be damaging?

Social search engines will let any web user track someone's social footprints across the web. For example favourite bands, potential purchases and even what they look like when they're drunk and partying hard.

In our age of social sharing, we expect some of our thoughts to be public. But as we slowly put more and more pieces of ourselves online, these specialised search engines are making it easier than ever to pull them together into a highly detailed (and potentially invasive) profile of our virtual lives.

I'll let you in on a little secret: the picture isn't always pretty. And even if there are no skeltons lurking in your closet, do you really want the world to know that you look at bad breath cures online or post awful Star Trek fan fiction?

The depths of the deep web

You hear a lot of terms bounced around when you talk about this growing breed of search engines. Some services like to be called 'social search' utilities, while others prefer the phrase 'people search'. Many boast of their ability to delve through the 'Deep Web' that even Google doesn't touch.

"Even though most people think the size of the web is basically the Google crawl index, there's actually a lot of information that Google doesn't crawl," says Harrison Tang, founder and CEO of Spokeo - which, taking a mash-up approach to its identification, describes itself as a 'social people search engine' service.

Spokeo, like its competitors Pipl and CVGadget, is designed to let you dig up information on friends, foes, and anyone in between. Spokeo goes a step farther than many of the other services, though, by importing your entire email address book.

Then, for a few pounds a month, it continually monitors your contacts and lets you know whenever anyone has done anything new, anywhere online. (The site's home page promises to help you "uncover personal photos, videos, and secrets" including "juicy" and "mouth-watering news about friends and co-workers".)

Each individual bit of information may seem insignificant, but the cumulative effect of seeing it assembled in a neatly packaged portfolio is enough to give almost anyone pause.

"Aggregated identity is actually a new type of identity," Tang says, theorising about why so many people seem to use the word 'spooky' when describing his service. "A lot of people know that they have a public MySpace page, a lot of people know that they have a public Twitter album. But, when combined together, it's not one plus one equals two - you actually create a new identity."

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  1. They know your darkest secrets...and they tell anyone
  2. How Spokeo works
  3. Electronic exposure

Social search engines can be a bit of a minefield. They can reveal your Amazon Wish List, photos of your kids, your musical tastes, and much, much more. What's even worse is they'll tell anyone too, and it could be damaging your online reputation, not to mention your credibility. We find out how you can protect yourself?

How Spokeo Works

Spokeo's system uses your contacts' email addresses to track their activity on a few dozen services, ranging from basic blogs and social networks to a slew of photo- and video-sharing sites. That means the random photos of your kids you shared on Flickr two years ago (or perhaps those less innocent images from your 18-30s holiday a decade earlier) will pop up right under your name, seconds after someone searches for you.

Less obvious sources such as Amazon Wish Lists, Spotify playlists and movie rating sites fill in the colorful details that you may not have realised were out there at all - things like an affinity for death metal or nose hair trimmers.

For sale: your information

Other services access the same data and then sell the information under the banner of marketing research. One highly visible example is Rapleaf, a company that describes its services as "data and people lookup".

Clients pay thousands of pounds to have detailed social profiles compiled of individuals in their own customer databases. As is the case with the data that Spokeo assembles, the information is all publicly available - Rapleaf just brings it together.

"Things that people have posted are out there for anyone to come and see," says Joel Jewitt, Rapleaf's vice president of business development. "As long as you're not going beyond that, that's within the privacy norms today."

Most of Rapleaf's clients, Jewitt says, are simply trying to understand how to use social media more effectively for marketing. A car manufacturer, for example, might want to know which models its customers are checking out and discussing on social internet services.

Armed with the company's list of customer email addresses, Rapleaf would crawl the web and track down the information, person by person.

"It's pretty standard web spidering," Jewitt says. "We re-create in an automatic way what someone from the general public would be able to do if they were looking."

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NEXT PAGE: Electronic exposure

  1. They know your darkest secrets...and they tell anyone
  2. How Spokeo works
  3. Electronic exposure

Social search engines can be a bit of a minefield. They can reveal your Amazon Wish List, photos of your kids, your musical tastes, and much, much more. What's even worse is they'll tell anyone too, and it could be damaging your online reputation, not to mention your credibility. We find out how you can protect yourself?

Electronic exposure

Whether they target businesses or individuals, the services have one thing in common: they build a highly detailed dossier about you solely from information that you yourself published - a circumstance that may give you a distinct feeling of discomfort.

"What it does is make the ubiquity of the internet and the sheer openness of the world tangible," says internet privacy expert Kevin B McDonald, executive vice president of Alvaka Networks, a network management firm. "It makes the whole concept of the world sharing of information and the 'no-walls' approach that the Internet was designed for very real to people."

The reality can be chilling if the information is going to certain interested individuals: a curious client, a boss big on background checks, or an obsessive ex, say. A recent study reported that half of all UK web users admitted to having used the internet to look up information on a former partner. The ease with which someone can arrange to monitor your every electronic move certainly adds a new dimension to the idea of fixation.

"It is a little 'stalkery'," says Marc Rotenberg, executive director of the Electronic Privacy Information Center. "If the information is distributed, that's actually a form of privacy. When it's gathered up in one place, it creates some new risks."

Rotenberg is no fan of companies that assemble nuggets of personal but public information to turn a profit. "The fact that someone's made something public doesn't mean that someone else can sell it," he contends. "I would say even with affirmative consent, if there's going to be a market for personal data, the user should get some percentage of whatever value the data has."

Taking control

The thing to remember, of course, is that these services aren't doing anything illegal. The information they gather is information that anyone who knew where to look - and had the time to do it - could find. So rather than ignoring the king-size file that may have been collected on you, McDonald suggests you should try to use it as a tool to understand and control your online identity.

"I've come to the point where rather than be driven by the internet, I intend to drive it to the degree that I can," he says.

"All you can do is learn to live with it," McDonald says. "That's the confines of the world that we live in."

PC Security advice

Broadband speed tester

  1. They know your darkest secrets...and they tell anyone
  2. How Spokeo works
  3. Electronic exposure

See also: 13 ways to improve your online reputation