MADRID, Spain?Campaigners are stepping up efforts to curb online tracking of Internet use by firms that deliver adverts tailored to the specific interests of consumers, as polls reveal widespread unease with the practice.

Corporations have always collected personal data on the people who buy their products but in the past this information came from sources such as magazine subscriptions and warranty cards, experts at a three-day privacy conference that wrapped up Friday in Madrid said.

Now it is flowing at breakneck speed into databases from multiple online sources, from dating services to newspaper websites, giving companies the unprecedented power to create detailed profiles of their customers, in many cases without their being aware of it, they added.

"There are so many grey areas in advertising that if the end user knew about it all, it would make their hair grey," said Jorg Polakiewicz, the head of the law reform department at the Council of Europe, a European rights watchdog.

The body is working on a new legal instrument on consumer profiling that it hopes will assist its 47 member states to better protect individuals from abuses, he added. So far only a few member states have legislation in place.

In the United States, Rick Boucher, the Democratic chairman of the House of Representatives' Energy and Commerce Subcommittee on Communications, Technology and the Internet, announced in September that he planned to introduce privacy legislation to regulate this so-called behavioral targeting of consumers.

The move toward greater regulation comes as surveys in the United States and Europe show that a majority of consumers on both sides of the Atlantic are against corporations monitoring their Internet use for marketing purposes.

Two-thirds of Americans object to targeted online ads, according to one of the first independent survey to examine the issue carried out by the University of California and University of Pennsylvania and published last month.

In the European Union 60 percent of people are concerned about the commercial use of data, according to a European Commission survey carried out in April, said Willemien Bax, the deputy director general of European Consumers' Organization BEUC which is pushing for tougher restrictions.

"It is very important that consumers are firmly in control of their personal data. I think it is unacceptable that our profiles are built up and we cannot see what they are," she said.

Some major corporations have reacted to the concerns by imposing their own limits on the use of online tracking of consumers.

Visitors to Web pages belonging to Procter & Gamble, the world's largest household products maker, "must opt in to have an online relationship" with the company, according to the firm's global privacy executive, Sandra R. Hughes.

The company also has set up a privacy education Web page and it provides consumers with examples of what kind of adverts and discounts they will receive if they agree to provide personal details.

But Jeffrey Chester, the executive director and founder of the Center for Digital Democracy, a US consumer watchdog group, said such efforts to self-regulate are largely a failure and stricter legal safeguards are needed.

"Self-regulatory schemes are inadequate, they fail to address the key issues," he said.