LONDON, England (CNN) -- More and more of us are sharing our personal details and chatting about our private lives on social networking Web sites, but what if these "chats" are not as private as we thought?
Social networking site Facebook boasts 39 million users.
Even listing something as innocuous as your favorite movies may leave you open to unwanted marketing, and your date of birth could even be a key for fraudsters to steal your identity.
Social networking sites are comparable to a global electronic village, and using them is akin to chatting to your neighbors over the back fence, sharing photos, gossip and updates about your social life. One such site, Facebook, now has 39 million users.
The information that we post about ourselves on the Web, called "digital litter" by technology experts, is a bonanza for fraudsters and marketing companies.
Details such as date of birth and where you work provide valuable clues for identity thieves, while status updates saying you are going on vacation could be tantamount to giving burglars the key to your house.
More information on your sexuality, religion, political leanings and favorite movies can provide a depth of detail to marketers that they previously could only dream of.
Issues of privacy and social networking sites are being addressed with some urgency by advocacy groups.
A soon to be added public search feature on Facebook will mean that user profiles can be found through search engines such as Yahoo and Google.
What was once a cozy world between friends (you had to join Facebook before you could access such information) is now available to anyone.
Facebook hopes the move will drive more users to the site and boost advertising revenues, which analysts believe are being under-realized.
Technology expert Om Malik wrote in his blog this week: "This move transforms Facebook from being a social network to being a quasi-White Pages of the Web."
He says one of Facebook's great features was privacy, but "that illusion might be ending soon."
Facebook representatives told CNN: "We are making public search listings available to give people who are not currently registered on Facebook the opportunity to discover their friends on the site. A public search listing only shows the name and profile picture."
Facebook's public search feature has raised eyebrows among security experts. As users have to "opt out" of the service rather than opt in, it could mean up to 39 million profiles becoming viewable when the service goes live.
Neil Monroe, External Affairs Director of Equinox, the leading online credit information provider, says social networking sites give yet another route for fraudsters.
"Fraudsters are taking advantage of the new craze for social networking," he said.
The Home Office in the UK also warns that "Internet fraud is one of the fastest growing areas of illegal activity in the UK."
Monroe says the wealth of information in social networking sites makes a criminal's job easier.
"The problem is that people don't realize the significance of the kind of information they are putting out on the Web and who may be accessing it. More and more consumers are signing up to these sites every day and chances are they'll put on their date of birth, location, email, job and marital status.
"Similarly, nearly all of us can search for the name of an old friend and find their personal details online without them even knowing. Fraudsters can use this information to steal an individual's identity and open accounts in their name."
While the Home Office publishes guidelines for consumers to protect themselves online, Monroe believes social networking companies have a responsibility to educate users about privacy.
"I would like there to be more done to control information but they are commercial organizations and I can understand they would want to introduce measures to allow them to expand."
Monroe believes users have a false sense of security on sites: "You wouldn't give that much personal information out to strangers or over the phone, so why do it online?"
Many people use their date of birth as banking passwords, so armed with this knowledge fraudsters might be able to apply for a credit card in your name or access your bank details.
Monroe is also alarmed at the cavalier approach we take to other people's privacy on the web.
"What's more frightening is that people are taking decisions about putting information up about other people -- such as publishing photos of them on the Web. It's a global consumer driven electronic village -- in a village people tend to know what you are doing. People need to be circumspect."
A marketer's dream
Privacy policies of many networking sites mean that information in your profiles cannot be sold on to a third party -- yet the "digital litter" we leave about ourselves on the Web can easily be collected, collated and used by marketers.
According to technology journalist Stefanie Olsen, some companies such as Repleaf (a privately owned start-up whose investors include Facebook backer Peter Thiel) have started to "sweep up all publicly available and sometimes hard to get information it can find on you on the Web, via social networks."
The information can then be packaged and sold as data to marketers so they can target customers with greater depth than was previously possible.
Social networking sites, e-commerce sites such as eBay and Amazon, photo collections in Flickr and the growth of blogging mean we are leaving more traces of ourselves online than ever before.
In the U.S., campaigns have started for the government to investigate privacy and marketing issues on social networking sites.
In the June report Google was rated the worst, and was branded "hostile" to privacy. The report also found Facebook had "substantial" threats to privacy for the way they dealt with user data.
"I don't like the direction where all this is headed. We are slowly leaving digital litter all over the web and some day it is going to cause problems," says Malik.
Monroe agrees: "I recognize its like trying to stop eBay -- it's a global phenomenon so it's going to be a global problem."
Equifax Top Tips for Using Social Network Sites:
• Don't include common verification such as your date of birth or your mothers maiden name
• Set up privacy on your profile so only close friends can view your information
• If you are going on holiday or you will be left in your home alone, don't put it on your site. This could leave you vulnerable to break ins
• Potential partners and employers are often searching names on these sites. Don't put anything on your site which could ruin your chances of a new job or boyfriend/girlfriend
• Be wary of anyone you meet on these sites. The photo may be deceptive and they may have different intentions E-mail to a friend