British Telecommunications PLC said Monday it plans to block its 2.7 million Internet subscribers from reaching child pornography Web sites banned under British law.
The system, named Cleanfeed, was undergoing trials and should be up and running in the next few weeks, retail chief executive Pierre Danon said.
Attempts to reach the sites will result in a "page not found" error message. BT said it will not see details of people trying to reach the sites, or of the sites themselves.
BT spokesman Ross Cook said the technology can block sites by filtering out either specific domain names or the unique numeric addresses associated with the Web server hosting the site. It can also block individual pictures on sites.
The numeric approach can potentially block legitimate sites that share the same hosting company as porn sites. But relying on specific names does little if sites constantly change their Web addresses.
Lists will be supplied by the Internet Watch Foundation, an industry monitoring group, and will be updated frequently. Cook said the foundation also would decide on the method and create an appeals process for sites that believe they are wrongly blocked.
Foundation officials did not immediately return a phone call and e-mail seeking additional details.
BT said it was talking with other service providers interested in buying the technology, but had no plans to market it commercially.
The company said it had the backing of the British government and police for the project.
Danon said because the system was based on a specific piece of legislation -- the 1978 Child Protection Act -- there was no risk of creeping censorship. Child porn sites are illegal under British law.
Western governments have grappled with how to block child pornography without resorting to censorship.
In the United States, civil liberties groups have fought Pennsylvania's attempts to force service providers to block access to child porn sites, saying such efforts also block thousands of legitimate sites.
Some governments have few qualms about restricting access to the Net. In China, government-installed filters bar access to thousands of Web sites abroad run by dissidents, human rights groups and news organizations.