Internet advertising is just the latest flashpoint in the privacy debate. It has been eight years since the F.T.C. has held a public workshop on the use of consumer data in online ads, and a lot of the hypothetical situations described then are now a widespread reality.

Image Credit... The New York Times

Many executives in the advertising industry do not see anything wrong with online targeting. They argue that the practice benefits consumers, who see more relevant ads. And they contend that for consumers, relinquishing some innocuous personal data is a small trade-off for free access to the rich content of the Internet, much of which is ad-supported.

“Why should the direct mail firms be able to target like that, and we’re not? All because it’s electronic?” said David J. Moore, chief executive of 24/7 Real Media, which is owned by the advertising conglomerate the WPP Group. “Ultimately, if you want the content to remain free on the Web, you need to at least give us the information to monetize it.”

But there is growing concern, even among online companies, about what information is being used to deliver ads to people.

“The market is getting edgier and edgier, and what is accepted in the marketplace gets dodgier and dodgier,” said Martin E. Abrams, the executive director of the Center for Information Policy Leadership at the law firm Hunton & Williams, a research organization financed by companies like Google, Microsoft and Best Buy. “We have really moved to a world where we say consumers need to police the market, and, increasingly, it is a harder world to police.”

Some observers say that many people do not really mind the targeting. Recent privacy surveys have found that younger people do not care as much about privacy as their parents do, but privacy groups say that is because people do not understand how much information is gathered.

“If people were shown all the stuff that’s been collected, I think they would be more appalled,” said Richard M. Smith, an Internet consultant who will speak on the F.T.C.’s opening panel.