The NSPCC is particularly concerned about popularity of social networking sites such as Bebo, Facebook or MySpace, which it says 52% of children aged 11-16 use once a day. Concerns have also been raised about YouTube where videos portraying bullying and other anti-social activities regularly surface.

The poll revealed that whilst just over half of the children polled had had a bad experience whilst online, they still believed that the internet was an important tool in their social development. Most young people logged onto social networking sites to talk to existing friends and to make new ones, with 60% of children using such websites to help combat loneliness, while 53% used them to share their problems.

The findings of the poll were unveiled as the NSPCC launched its Don't Hide It campaign, which aims to encourage children to speak out about all forms of abuse carried out on social networking websites.

Speaking to the BBC, NSPCC director and chief executive Dame Mary Marsh said: "Children face real threats on the internet such as sexual grooming, cyber-bullying, exposure to violent, pornographic and other unsuitable material. Online social networking is part of millions of children's lives. We must recognise and respond to this reality by helping them be safer online as well as helping them speak out about abuse at the same time."

Also speaking to the BBC, Jim Gamble, Chief Executive of the Child Exploitation and Online Protection Centre, said an increasing number of children were putting their lives online. He said: "The NSPCC research matches our understanding of the problems that children and young people are vulnerable to online. The rise in popularity of social networking sites, online gaming and chatting on instant messenger means that more young people than ever are sharing their personal experiences and details with strangers. In the virtual world the need for cautiousness is often forgotten. The warning signs traditionally associated with strangers are lost amongst the possibility and excitement of new relationships."

Previous research by the NSPCC revealed that 46% of children had given out personal details about themselves to people they have met online, such as photographs and phone numbers. The charity has advised that nobody, especially children, gives out such information to anyone they have met online, and that children should not reveal their real name.