Four out of 10 Facebookers (41 percent) agreed to become "friends" with a fictional character, allowing him access to critical personal data.

The character's creators, Sophos, have consequently published new research into the risks of identity and information theft via Facebook, reports MarketingCharts (via CNET News Blog).

Users often divulged personal information - email address, date of birth and phone number - to the stranger, greatly increasing their susceptibility to ID theft, Sophos said.

Sophos' "Facebook ID Probe" involved creating a fabricated Facebook profile, then sending friend requests to 200 randomly-selected persons across the globe.

The profile page was for 'Freddi Staur' (an anagram of "ID Fraudster"), a small green plastic frog who divulged minimal personal information about himself.

In the majority of cases, Freddi gained access to photos of family and friends, information about likes/dislikes, hobbies, employer details and other personal facts, such as date of birth. Many users also disclosed the names of spouses or partners.

"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," quipped 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," Cluley said.

"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."

"It's important to remember that Facebook's privacy features go far beyond those of many competing social networking sites. 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," Cluley concluded.

MarketingCharts provides additional findings from the study.