The next time you are about to register as a user with a Web site, think again. Think hard. As an on-line consumer, there are good reasons to be worried about what happens to the data you part with to gain access to a site. At a talk at Internet World Asia on 'Effective Advertising Through Targeting', Web advertising executives confirmed fears Web surfers are at risk of enjoying less privacy than they realise. On-line ad networks such as Doubleclick and 24/7 Media put ads on Web sites for users to look at based on the Web pages they visit the most - considered an indicator of their personal interests. When asked if such advertising networks, as well as portals such as Yahoo!, could potentially pool that information along with the personal data given by registered users to Web sites, a guilty silence filled the air. After a moment, Colin Macintosh, managing director of Space Media Asia, grinned and said: 'Yes, there is definitely that danger. It is very real.' Doubleclick and 24/7 Media Asia have partnered with content portals Asiacontent.com and China.com, respectively. Partnerships such as these mean an advertising network could easily share user tracking information with the database of registered users of the Web sites its sister company operates. That could allow the companies to know not only a user's name, and the personal information he typically discloses upon sign-up to a Web site, such as address, telephone number, income level, but also to pinpoint his likely consumer interests. That is extremely powerful for advertisers wanting to target likely customers, and could help Web advertising become a US$1.5 billion market by 2001. But it could also contravene SAR privacy laws set out by the Government's Privacy Ordinance. A spokesman for the Privacy Commissioner's Office yesterday declined to comment on whether this advertising technology contravened privacy laws, saying it needed to study the issue further. 24/7's Asia-Pacific managing director Patrick Wong agreed such pooling of information without the user's knowledge would probably be illegal in Hong Kong. But he said there would also be strong commercial reasons for 24/7 not to share information with parent company China .com's Web sites. 'We would absolutely not do it,' Mr Wong said. 'It would jeopardise our position as an independent ad network. 'We have to maintain independence if we want to sign up competing portals as customers.'