Shares in Internet advertising technology firm Phorm took a tumble after telecoms giant BT opted not to proceed with trials of Phorm's Webwise technology.BT, which has 4.8m broadband customers, said the decision was taken to enable it to focus on "our public commitment to developing next-generation broadband and television services in the UK."The company's decision may also have been prompted by consumer resistance to Phorm's technology, which many opinion formers on the Internet regard as "invasive". Phorm's Webwise product tracks a user's browsing habits anonymously and uses the information to target the user with more relevant advertising.Other big UK internet service providers (ISPs) such as Carphone Warehouse's TalkTalk and Virgin Media have expressed an interest in using Phorm's technology, which could provide them with a lucrative income stream. Opponents of the Phorm software argue that the ISPs have no right to earn income from a user's browsing history.Phorm said it remains committed to deploying its technology in the UK and that discussions to this end are still in progress. However, given the slow pace of progress in the UK the company has shifted its emphasis on to overseas expansion after losses rose by about 50% last year."We have already minimised our dependency on the deployment by any single ISP or in any particular market. In addition to making excellent progress in South Korea, we are engaged in more than 15 markets worldwide including advanced negotiations with several major ISPs," the company said in a statement.