Phorm’s targeted advertising has been blocked by a number of websites including Amazon.

Leading online retailer Amazon has opted out of the advertising system branded as Webwise, developed by technology company Phorm.

Phorm specialises in delivering behaviourally and contextually targeted advertising that relies on scanning a user’s web browsing activity, yet has faced considerable debate over the way that users give consent for this profiling.

However, the technology does differs from other behavioural advertising systems which tend to use data only from partner websites visited by users and do not work in conjunction with ISPs; Phorm’s partners include leading Internet Service Providers (ISPs), Publishers, Ad Networks and Advertisers.

The firm has recently completed trials with BT’s customers, and Talk Talk and Virgin have an expressed an interest in the service.

The system assigns a unique, randomly-generated number in a cookie to a customer’s browser to preserve anonymity, then matches the categories of browsing activity with advertising. When there is a match the customer sees the more-relevant advert.

It avoids any information that might identify a user personally, its cookies are anonymous, and never keeps records of individual websites that were visited or what someone is doing on the web.

The Open Rights Group wrote to seven of the world’s leading websites last month – Microsoft, Google/Youtube, Facebook, AOL/Bebo, Yahoo, Amazon and eBay to ask them to block Phorm’s attempts to profile their sites.

Jim Killock, Executive Director of the Open Rights Group, said: “We expect more sites to block Webwise in the near future and also ISPs to drop plans to snoop on web users.”

Three other sites, LiveJournal, mySociety and Netmums have also contacted the Open Rights Group to say they too would be blocking Phorm’s technology.

Earlier this week the European Commission said it was starting legal action against the UK over its data protection laws in relation to Phorm’s technology.

However, in a statement on 14 April, Phorm responded that its technology is fully compliant with UK legislation and relevant EU directives.