Not all case of identity theft come from stolen notebook computers or vulnerable computer networks. Computer security firm Sophos says many members of the social networking site Facebook fail to take simple steps to guard against identity theft.

Compiled from a random snapshot of Facebook users, Sophos's research shows that 41 percent of users, more than two in five, will divulge personal information - such as email address, date of birth and phone number - to a complete stranger, greatly increasing their susceptibility to ID theft.

The Sophos Facebook ID Probe involved creating a fabricated Facebook profile before sending out friend requests to individuals chosen at random from across the globe.

To conduct the experiment, Sophos set up a profile page for 'Freddi Staur' (an anagram of 'ID Fraudster'), a small green plastic frog who divulged minimal personal information about himself. Sophos then sent out 200 friend requests to observe how many people would respond, and how much personal information could be gleaned from the respondents.

Freddi may look like a happy green frog that just wants to be friends, but actually he's happy because he's just encouraged 82 users to hand over their personal details on a plate, said Graham Cluley, senior technology consultant at Sophos.

While accepting friend requests is unlikely to result directly in theft, it is an enabler, giving cybercriminals many of the building blocks they need to spoof identities, to gain access to online user accounts, or potentially, to infiltrate their employers' computer networks.

Among the findings of the Sophos Facebook ID probe:

• 87 of the 200 Facebook users contacted responded to Freddi, with 82 leaking personal information (41% of those approached)

• 72% of respondents divulged one or more email address

• 84% of respondents listed their full date of birth

• 87% of respondents provided details about their education or workplace

• 78% of respondents listed their current address or location

• 23% of respondents listed their current phone number

• 26% of respondents provided their instant messaging screenname

In the majority of cases, Freddi was able to gain access to respondents' photos of family and friends, information about likes/dislikes, hobbies, employer details and other personal facts.

In addition, many users also disclosed the names of their spouses or partners, several included their complete rsums, while one user even divulged his mother's maiden name - information often requested by websites in order to retrieve account details.

What's worrying is how easy it was for Freddi to go about his business. He now has enough information to create phishing emails or malware specifically targeted at individual users or businesses, to guess users' passwords, impersonate them or even stalk them, Cluley said.

Most people wouldn't give out their details to a stranger in the street, or even respond to a spam email, yet several of the users Freddi contacted went so far as to make him one of their 'top friends'. People need to realise that this is still unsolicited communication, despite it occurring within Facebook, and users must employ the same basic precautions - such as not responding in any way - to prevent exposure to wrongdoers.

As well as the successful friend requests, a number of users unwittingly enabled Freddi to gain access to their profile information simply by sending response messages such as "Who are you?" and "Do I know you?" back to his Facebook inbox.

Sophos experts note that users' profiles can be protected from such exposure by adjusting the privacy controls within their Facebook account settings.

It's important to remember that Facebook's privacy features go far beyond those of many competing social networking sites, Cluley said. This is about the human factor - people undoing all that good work through carelessness and being preoccupied with the kudos of having more Facebook friends than their peers, which could have a serious impact on business security, if accessed in the workplace.