Microsoft's internet service MSN is to cut back drastically its chatroom services because of concerns about child safety, it said.
One in five children regularly use chatrooms, reports suggest
MSN is closing all its chatrooms in Europe, the Middle East, Latin America and most of Asia from 14 October, and changing the way others are operated globally.
"As a responsible leader we feel it necessary to make these changes because online chat services are increasingly being misused," it said.
Children's charities welcomed the move as "momentous" and said they saw it as a big step towards protecting young web users, but some have criticised the decision.
Internet service provider Lycos has branded the action as "irresponsible" and fear children will move to other unmoderated chatrooms on the net.
Some have suggested that MSN may have economic reasons for closing down their chatrooms.
MSN UK's Matt Whittingham told BBC News Online it was not a decision they had taken lightly.
MSN GLOBAL CHATROOMS
US: Unmoderated chatrooms will be credit card subscription only and bundled with other products
Canada, Australia, Japan: 24-hour moderated chatrooms, with some unmoderated behind subscription
New Zealand and Brazil: 24-hour moderated chatrooms
UK and Europe: All chatrooms closing
Middle East, Latin America, Asia: All chatrooms closing
"We have been concerned about chatrooms for a while and reached a stage where we were no longer prepared to put up with inappropriate communication," he said.
The only chat service available to MSN users in the UK will be the free instant messaging service, MSN Messenger, which is not so open and gives people more control over who they talk to.
Chatrooms on MSN's other global sites will either be supervised - or moderated - by an adult 24 hours a day, or will be on a credit card subscription-basis only.
It means no free, unmoderated chatrooms will exist anymore on any of MSN's global network of sites.
There has been growing concern among experts that the anonymity of net chat means young people are being targeted by adults pretending to be children.
"We have seen cases where under-16s have been approached by people pretending to be same age, but who are grown adults trying to solicit young people for abusive contact," Mr Whittingham explained.
He added that, although most messages in chatrooms were not inappropriate, a "small minority" had spoilt chat for people of all ages.
People have also been increasingly targeted by spammers posting hundreds of messages and inappropriate web addresses to chatrooms.
Many have been "mining" rooms for data, finding out users' e-mail addresses to build spam lists.
MSN has acknowledged that some chatters will not be happy about the move.
"We regret responsible users will be affected by this move, but we looked at this very carefully and on balance to safeguard customer interests," said Mr Whittingham.
By only making instant messaging available, chatters will be able to restrict and control who they talk to because they can only chat to people on their "buddy lists".
CHATROOMS AND CHILDREN
One in five children aged nine to 16 regularly use chatrooms
More than half have engaged in sex chat
A quarter have received requests to meet face-to-face
One in 10 had met face-to-face
Source: Cyberspace Research Centre, July 2003
People need to ask permission to be a "buddy" and they need to know the user's e-mail address to make a request, which means most children only have "buddies" who they know outside the internet.
They will also continue to make MSN Messenger free to users.
Mr Whittingham said all net services offering chatrooms should continue to look at how they can safeguard everyone on the internet, ensuring young people and parents stick to common sense advice.
This means never giving out personal information online, and never arranging to see someone they have met online in the real world.