Children use false identities to outfox parents monitoring them on-line.
Whatever the situation, social networking sites such as Facebook are a source of anxiety for parents, and a new study will only add to their alarm. Children are staying way ahead of attempts by parents and schools to police their online activity, the study suggests. And the latest ruse is a secret, fake-name Facebook account.
"Some kids will have two or even three," says Dr Barbie Clarke, of the youth research agency Family Kids and Youth, which conducted the research after monitoring online trends among a sample of schoolchildren in the UK.
"Their habits change and we're seeing them progress from the obvious lie about their age - allowing them to use Facebook in the first place - to this second or third identity. It's usually driven by mum picking up on something from their page and raising it with them. They want privacy and they want a secret world. A false identity can be used for nastiness, to anonymously bully, but generally it's about secrecy - like a secret diary, or dialogue they can have away from parents and other family members."
Many children use school facilities to access their fake accounts. "I have two," admits Harriet, 14.
After she upset a fellow student with a posting she says was "meant as a joke", her mother banned her from using the site.
"I tell everyone my new name and get loads of friends as soon as," says Harriet. "My mum is on Facebook and she'd see if my name was up. I don't do it on our computer at home, only at ICT in school and on my iPhone.
"It's not as good on the iPhone for seeing pictures, but you can use it late at night in bed. You can't not be on it, or you just don't have friends."
Concerns over children setting up Facebook accounts and lying about their age are not new. Facebook's terms and conditions, which were put in place to comply with US law, are unenforceable in practice.
Peter Bradley, deputy director of the anti-bullying charity Kidscape, says: "There's enough evidence from inquests or helplines to show parents aren't scaremongering. With devices getting smaller, it's harder to see warning signs."
Many schools fail to monitor pupils' use of technology, hesays. "It's the biggest issue we have, schools not taking parents' concerns seriously."
But Clarke cautions against alarmism. "I think there is a lot more fear among parents than there need be. Actually, children are quite supportive of each other most of the time. It's the lonely, isolated child we need to worry about. Of course there are issues with bullying - there always have been and there always will be. Technology makes it much more immediate and personal."