People who use internet networking sites are being warned that they could be at risk of identity theft.
Actor and writer Stephen Fry has a Facebook entry
Credit information group Equifax said members of sites such as MySpace, Bebo and Facebook may be putting too many details about themselves online.
It said fraudsters could use these details to steal someone's identity and apply for credit and benefits.
About 80,000 people in the UK were victims of identity theft last year, at a cost to the economy of £1.5bn.
Neil Munroe, external affairs director for Equifax, said: "Fraudsters are taking advantage of the new craze for social networking.
"The problem is that people don't realise 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, e-mail, job and marital status.
"Fraudsters can use this information to steal an individual's identity and open accounts in their name."
The group advised people to limit the personal information they make available about themselves online.
It said people should avoid putting their full date of birth on one of the sites, as well as the names of children or pets as these are often used as passwords.
Mr Munroe said: "We don't want to stop people using these sites, but we do advise them to limit the amount of information they make available to stop people stealing their identity."