A proposal to create net domains ending .xxx has been approved by the body that oversees the Net's addressing system.
Sexually explicit sites will be encouraged to move to the new domains to make it easier for people to filter and avoid them.
The .xxx approval reverses earlier decisions to block it over fears that it would be ineffective and controversial.
Net domains such as .com., org., .uk and so on are overseen by the Internet Corporation for Assigned Names and Numbers.
Icann polices the firms that run the different domains and approves the gradual expansion of the pool of net names that can be used.
In 2000 Icann approved seven new domains but the Net's original generic domains such as .com, .org and country names such as .uk are still the most popular.
Many of the new domains that Icann has approved are for specific industries or special interest groups.
More recently Icann has been considering a second list of proposals for new sponsored domains.
Earlier this year it officially approved the creation of the .jobs and .travel domains.
The .xxx domain is the latest sponsored domain to win approval. Icann is now negotiating with ICM Registry, backers of the .xxx plan, on how the new Net destination will be funded and run.
ICM Registry was formed specifically to lobby for the creation of the .xxx domain. Moving to the .xxx domain will be entirely voluntary but ICM said that some pornographers have expressed support for the idea.
In a statement, ICM said the creation of the .xxx domain would: "help protect children from exposure to online pornography and also have a positive impact on online adult entertainment through voluntary efforts of the industry."
While ICM will handle the technology behind .xxx, sites using it will be overseen by the non-profit International Foundation for Online Responsibility.
The decision to approve the .xxx domain comes five years after the idea was first proposed.
Icann has rejected the proposal on several occasions before now. In an early report on the idea, Icann experts said the proposal did not "meet an unmet need" because adult content was readily available on the Internet. A report on the proposal noted: "no mechanism (technical or non-technical) exists to require adult content to migrate from existing [domains] to an .xxx [domain].
Icann experts also questioned how easy it would be to determine which sites should use .xxx and which avoid it.
"A lot of people objected because they said the domain naming system shouldn't be used as a content filter," said Jonathan Robinson, business development director at NetNames.
"To my mind though it's quite an elegant solution," he said.
ICM Registry might face problems in getting people to sign up, said Mr Robinson.
"If you have a very successful porn site running off a particular domain name you are going to be reluctant to change that," he said.
Icann also rejected the idea because of worries that eventually all sites dealing with sexual matters, including sex education sites or those that support victims of sexual abuse, would be forced to use the .xxx domain and, as a result, be harder to find.
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