Nearly one in three UK children have not had any lessons on how to use the internet safely, a study suggests.
The more net-savvy children are more at risk, the study found
Those most at risk of encountering pornography or paedophiles were the most expert computer users, the survey of nine to 19-year-olds found.
They entered sites more adventurously, ignoring safety concerns, London School of Economics researchers said.
Those who stuck to a narrower range of sites were less likely to be exposed, the survey of 1,500 young people added.
Even children whose internet use was supervised by their parents were not protected from the dangers.
The number exposed to internet porn, bullying and invasions of privacy was likely to rise without greater efforts to make internet use safe.
Professor Sonia Livingstone, who conducted the research, said: "We are talking about contact risks, children giving out personal information online, going into chat rooms without knowing the safety rules and possibly meeting people they first met in a chat room."
She added: "We began with the assumption that as children use the internet and became more skilled they would manage to avoid the risks.
"We found the opposite was true."
The research involved a series of focus group discussions and a UK-wide survey.
It found children who avoided the risks were able to do so "by making only a narrow and unadventurous use of the internet".
Prof Livingstone said: "Restricting children and young people's internet use reduces the risks but also carries a cost because it reduces their opportunities online.
"It is of concern that even the most skilled young people are not avoiding online risks.
"If we want to make sure that in five years' time young people aren't at greater risk online, more effort is needed to make the internet safer for them."