29/02/2012 17:06 GMT | Updated 29/04/2012 06:12 BST

For Sale: Your Digital DNA

With Google announcing a change to its privacy settings - and the subsequent uproar it caused - it highlights an alarming trend of how easily our identities online are bought and sold, without our knowledge.

If you've ever posted a photo on Facebook, used social networking, posted a comment on any website, published anything or played one of the millions of apps currently floating around Apple's app store, then chances are, you've been hacked.

Not by a legion of super spies locked away in a secret location doing the dirty work of the government. Nor are your details being used by a terrorist organisation to buy nuclear weapons on the black market - although they could be.

Your details are being used by sources far closer to home and by companies with better resources and technical know how then some band of 'freedom fighters' living in a cave. Do you know what the worst thing about all this is? You're letting them.

Your "digital DNA" is everything you've ever written, every site you've logged on to and every drunken moment you've shared with friends. According to a study conducted by Microsoft, just 42% of people in the US - and just 36% in the UK - have googled themselves or taken time out to explore the reams of data that currently exist online about you.

While that may sound like a strike against vanity, in reality, being ignorant to how freely personal information flows across the web could mean your digital identity is being shared, bought and sold, with your express permission.

One of the most popular users of your private data over the last few years has been both your current and your future employers. According to a survey of 450 businesses carried out by over half used social networking sites to research potential candidates, with another 12% planning to do the same.

While some Facebook users have attempted to combat this by turning their profiles to "private", people are still capable of seeing your details who aren't your friends, explains professor Pamela Wik-Grimm, a teacher of Tools for Internet Users in New York. "You might be having what you think is a private chat, but it could end up being forwarded or posted publicly." As long as someone in your friends network has an open privacy setting it means businesses can see easily follow a thread through friends' Facebook pages and find you.

It's not just business who are actively seeking you out online, your insurance provider is also snooping round looking for clues to better predict your next bill.

A report published in 2010 by Deloitte Consulting LLP found using people's online data was as effective in detecting potential health risks as a blood or urine test. So compelling was the paper, that several insurance companies, including Aviva and Swiss Re: have already started using it - although Aviva in the UK are still considering whether to follow their US counterparts. "Insurance analysts have found common factors within the friendship groups, interests and family backgrounds of people living beyond 100," says Craig Beattie, an insurance analyst with Celent consulting. "If you are selling someone life insurance, it's very useful to know if they have these indicators and insurers can find it just by looking at the person's Facebook profile."

With the incredible growth of the internet and our desire to share more data with our friends than ever before on new social networks, the rules for what can and cannot be used to turn your identity in to cash are essentially being made up as we go along.

Facebook is now required to have bi-annual audits on its privacy settings, and Google's recent privacy changes - it now wants to be able to move your identity and habits across all of its platforms - has already come under criticism.

IT research and consulting firm Gartner is advising private sector enterprise clients that use Google Apps to review their contract with Google to make sure it contains language that shields their organisation from potentially negative effects of this new privacy policy.

However, this is the tip of the iceberg when it comes to your digital footprint - and while large corporations like Facebook and Google are finally being scrutinised for how they use our data, there are still thousands of smaller, less obvious ways our identities are being traded.

So the next time you hand over your email address or username, be advised that not everyone has your privacy as a priority.