Generations of parents have nagged their teenagers to turn off the TV and find something better to do.
Now, it seems, their children may be doing just that.
Do you know someone who spends hours chatting online?
Chatting with friends online - via services like MSN and Bebo - is beginning to take over from watching TV as the main hobby of many young people.
Much of the chat is happening in so-called "closed community websites". Unlike chatrooms, they're not open to everyone: each person has to be invited to join in.
So, is online chat a good thing - and how safe are closed community websites?
This morning on Breakfast
We found out about life online with pupils from one school at Whitefield, greater Manchester
We discussed the spectacular rise of closed community websites with the Chief Executive of Bebo, Michael Birch - and with a government internet safety advisor, Dr Rachel O'Connell
And, we asked for your views
WHAT NOT TO DO ONLINE
Never reveal name, address, phone number or password
Never reply to nasty or suggestive messages
Never open e-mail attachments unless they come from someone you trust
Never meet anyone unless an adult goes with you
Growing numbers of teenagers are spending hours at a time online, chatting to their friends.
MSN is popular with many teenagers - but the fastest-growing service is Bebo, launched only eight months ago.
It sets a minimum age of 13 for participants - and its website does contain safety advice - including a warning to be careful about divulging personal information and arranging to meet cyber friends offline.
Parents and teachers worry that, however well-policed, online chat can be used for bullying, in exactly the same way as text messages.
Some schools have also expressed concern over the amount of time teenagers spend online, instead of doing their homework.