UK telecom BT is dipping its feelers back in the behavioral advertising market. The company has decided to re-test Phorm, whose technology enables participating websites to serve ads to users, based on web-surfing data provided by their ISPs. Revenue is split between the ISP, website publishers and Phorm.

BT courted media contempt when it ran two secret Phorm trials between 2006 and 2007. Discovery of the trial sparked the ire of privacy advocates, which launched a behavioral advertising witchhunt in both the US and the UK.

Phorm's American counterpart, NebuAd, suffered most from negative press and Congressional probes. The company recently lost its CEO and decided to change its business model entirely.

Phorm has been more fortunate. By defending itself vigilantly against detractors, committing to give users the option to opt out (a stance that did not work for NebuAd), and hiring a prominent lobbying firm to represent its interests on Capitol Hill, the company managed to receive a nod of approval from the UK government.

Beginning September 30, a sample of 10,000 BT customers will be invited to opt in to a Phorm trial. Opt-in options will appear to users through a pop-up ad. The resulting pilot will last about four weeks.

"If it goes according to plan it's our expectation that we will roll it out across the entire broadband customer base," said a spokesman for BT, who claims Phorm's technology won't just serve more relevant ads to users; it will also help them avoid fraudulent websites. (Users will be warned through the ad system when they are about to visit a page that's been flagged as dangerous.)

To keep privacy advocates at bay, BT is also preparing a system that enables people to opt out at the network level.

Users will be reminded of the test just before it begins.