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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