More than half of children in the UK using the internet have had an "unwanted experience", a poll suggests.
The NSPCC found 50.4% of 2,053 children had experienced problems such as bullying, being threatened or sexually harassed while online.
It is concerned about the popularity of social networking sites such as Bebo or MySpace, which it says 52% of children aged 11-16 use once a day.
NSPCC chief executive Dame Mary Marsh said: "Children face real threats."
The survey indicated most young people logged onto such websites to make new friends and link up with people they already knew.