Parents are unaware of the dangers their children face by posting details about themselves on social networking sites, according to research commissioned by Ofcom.

The survey of 5,000 adults and 3,000 children found that nearly half of children aged between eight and 17 have a profile on one or more of the popular social networking sites.

Although Bebo and Facebook set a minimum age limit of 13 years old, and Myspace 14 years, the research found that more than a quarter of eight- to 11-year-olds in the UK have used the sites.

Ofcom said it found younger children lied about their age to bypass these restrictions.

Despite two-thirds of parents saying they set rules for their children regarding the use of social networking sites, one in five parents said they were unaware that their child may have made their profile public.

Robin Blake, head of media literacy at Ofcom, said: “When their children go out to play, parents often state ground rules about when they come back and when to meet and so on. Parents need to recognise that going online has the same kind of risks."

He said the websites, many of which are based in the US, could do more to remind people of the risks involved in putting all their details online.

Currently Myspace, Bebo and Facebook all say they remove the profiles of users that are found to be too young from their sites. But at present no technology is used to actively verify the age of users.

The Home Office is expected to announce a voluntary code of conduct for social n etworks this week.

This code will ask Bebo, Myspace and Facebook to set high privacy settings as a default if a child is under the age of 18. It may also ask that sites maintain a contact page listing emergency contact numbers where children can get help if they feel they are in danger.