OpenDNS will this week launch a user-powered web categorisation and filtering service modelled along the lines of its PhishTank anti-scam service, with the aim of making web filtering more accurate and accessible.

The service, making its debut on Wednesday, is intended to help users and system administrators block sites that might be dangerous or undesirable, as well as helping users find their way around the Internet.

OpenDNS made its debut in 2006 with a customised DNS service.

Later that year it launched PhishTank, which works on a principle similar to collaborative bookmark sites such as Digg, allowing registered users to submit and vote on the validity of phishing URLs. PhishTank data is now licenced by organisations such as Yahoo and Mozilla.

OpenDNS now hopes to build on this model with its web content filtering system, allowing registered users to categorise a site as "gambling," "video sharing," "social networking," or more controversial labels such as "hate" - a total of 30 categories, to start off with.

Other users will be able to vote on the accuracy of the submitter's tag. "There's a trust metric built in, so the more you vote and the more accurate your votes are the more weight they carry," an OpenDNS spokeswoman said.

Once a tagged domain crosses a certain threshold, it will be added into that category in the OpenDNS system. More categories will be added as they are requested, the company said.

OpenDNS argues the system will be more comprehensive than top-down filtering systems, with tens of thousands of users submitting and verifying the accuracy of categorisations.

It will also be able to handle changes and new websites in real time, as opposed to other services which typically update once a day. Moreover, the service will be free of charge, which the company argues is a better model for such services than making users pay "protection money."

"By making a safe Internet available only to those who can afford it, you give the bad guys an advantage and cripple the Internet's potential to be a medium that connects people to information," said the spokeswoman.

OpenDNS offers an alternative to ISPs' default domain name lookup services, promising faster web surfing and anti-fraud services.

The filtering service, like PhishTank, will also be delivered via the custom DNS service, which is free of charge. OpenDNS' revenue model is based on selling advertising, which is displayed when users type an incorrect address.