Social networking sites such as Facebook and MySpace are becoming a magnet for identity thieves. That's according to internet experts who say the personal information posted could be enough to apply for credit cards or a bank account. And, because so many users give details of their present location, they're also advertising when they are away from home.

"The underlying philosophy is [to] realise that your PC isn't protected unless you do something about it and your personal information is as valuable to criminals as it is to you," says Tony Neate, Managing Director for Get Safe Online . "In the same way that you wouldn't leave your wallet and passport in an unattended, unlocked car; don't leave your personal data unprotected."

But it's certainly not just adults that are at risk. A recent report, commissioned by Garlik , has shown that the boom in social networking has also exposed children to a number of dangers such as cyberbullying, grooming and fraud. According to the report, one in five UK youngsters have met up with someone they found online. One in twenty have done so regularly.

Garlik also found that four in ten teens regularly visit sites specifically prohibited by their parents. Many hand out personal details, too. 30 per cent divulged their full name, 12 per cent their address, 20 per cent their mobile number and 46 per cent their school name.

More than half admit they surf the internet without their parents knowing. "Our research is a shocking wake-up call to all parents in the UK to sit down with their children and talk about how to keep safe online," says Tom Ilube, CEO of Garlik.

"The Web is a wonderful place to explore but young people continue to make themselves vulnerable by not applying the same caution online as they would in person."

Meanwhile experts are also warning about the threat through internet-enabled mobile phones. "While the internet is generally accessed at home via the family or individual child's PC, how many parents think about the access their child may have via their personal mobile phone?" says AdaptiveMobile 's Lorcan Burke.

"Although not immediately obvious, the mobile phone poses a more serious problem than PCs as they are an inherently more private medium and are harder to police. One in four children in the UK own a mobile phone. By the end of the year the average age a person will acquire their first mobile phone is expected to be eight years."

Garlik's report found that 20 per cent of eight to fifteen year olds surveyed had given out their mobile numbers online.

Garlik's top tips for parents

1. Keep internet-connected computers in a central and open location, particularly for younger children.
2. Sit down and talk to your children about their online activity. You should know everyone on your children's contact list.
3. For younger kids, make sure you know all their passwords. Don't intrude, but let them know that you know, just in case.
4. Tell your children not to provide personal details online. No full names, addresses or telephone numbers.
5. Devise a code of conduct - a list of internet rules - that you and your children agree to sign up to.