Children and teenagers who send sexy images of themselves to their boyfriend or girlfriend have been warned to "think before you send".
A hard-hitting video shows the dangers of so-called "sexting" after the Beatbullying charity found one in five 11 to 17-year-olds has received a sexually explicit or distressing text or email, with 70% admitting they knew the sender.
Exposed, a 10-minute film by the Child Exploitation and Online Protection (Ceop) Centre, shows a teenage girl distressed after indecent images she sent to her boyfriend appear on the internet.
She stresses she can never take back what has happened and warns others to watch what they send in texts and emails, saying anything sent and shared can become "public and permanent", affecting lives and even job prospects.
Peter Davies, Ceop's chief executive, said: "We know that young people are increasingly using technology not only to stay in touch, but to explore their sexuality and to push the boundaries in what they send and to whom they send it. It is now so easy to send pictures instantly via emails and texts that we are seeing instances of boys or girls sending sexual images of themselves to others without considering the consequences.
"They often find out later that the image has been passed on to many others and as a result they can be the victims of bullying or harassment. In some rare instances we have seen these images end up in the collections of offenders."
Crime Prevention Minister James Brokenshire added it was a "worrying trend".
"We should encourage young people to use technology but it's really important that they are made aware of the dangers involved too," he said.
Beatbullying worked with 2,094 young people for the survey, which was carried out in 2009.
The video is available at www.thinkuknow.co.uk/teachers.