Children across Europe are being exposed to online threats but remain apathetic to the risks, according to research by EU Kids Online.
The findings, collated from research published in 21 European countries, suggest that social networking is a large part of the problem.
Uptake spread rapidly across the whole of Europe last year and, even in countries where the internet has arrived more recently, such as Estonia, more than two thirds of high school students use social networks.
But, despite the many benefits of social networking, EU Kids Online warned that the phenomenon presents a threat to teenagers' privacy and well-being.
The research revealed that many young people are giving out personal information online which can leave them exposed to identity theft and abuse.
"Although children and young people are delighted with the opportunities open to them on the internet, especially for social networking, many of them are giving out personal information without realising who might see it," said Professor Sonia Livingstone, director of EU Kids Online.
"Our research has found substantial amounts of bullying, harassment and unwanted sexual messages, which is very distressing for some."
Anti-malware firm PC Tools said that, although it supports attempts to educate children, many of the measures being proposed will not make any difference unless the lessons are carried through to everyday internet and online etiquette.
"We are all hoping that research such as this will drive parents and young web users to recognise and understand the dangers of the internet," said Mike Greene online security expert at PC Tools.
"Naivety and indifference fuel online crime through a mix of poor etiquette and out-of-date protection, so it is imperative that parents and young users sit up and take notice."
Greene added that the 'it won't happen to me' attitude is the root cause of many problems, as young internet users leave themselves and their PCs exposed to botnets, spyware and viruses.
"Our own research of 25,000 users found that an alarming 50 per cent of UK consumers continue to download and file-share regardless of the known risks," said Greene.
"This is despite the fact that 80 per cent of respondents had reported that their computer had been infected by malicious threats."
The EU Kids Online research found that the Czech Republic has the highest number of online teenagers who have given out personal information to a stranger.
Nearly 91 per cent had given out an email address, 79 per cent a photograph and 72 per cent a phone number.
The report concludes that advice and guidance to teenagers is sorely needed, especially in countries new to the internet or where teenagers' experiences are ahead of their ability to cope.
Greater care is also needed in targeting advice depending on cultural and individual circumstances when it comes to giving out personal information online.
EU Kids Online believes that social networking sites could do more to advise teenagers about their privacy and ensure that they understand the implications of disclosing personal details.
