If you're reading this in the newspaper, you can look around, flip the pages, and find plenty of ads. You can also be reasonably sure how those ads got there - companies trying to sell you stuff want you to know who they are.
If you're reading this online, that last assumption isn't so clear.
Sure, a Lexus ad is a Lexus ad, in print or in pixels. But if you've been reading reviews of that snazzy GS Hybrid, and then looking online for an auto loan, you may begin to wonder exactly what the advertisers know about you - especially if the ad seems to follow you from site to site.
That's a classic example of "behavioral marketing," and a fairly benign one. If you want the car - and who wouldn't? - you may welcome the ads. Besides, there's nothing deeply personal about them.
But what if you started seeing ads for impotence remedies, or bankruptcy lawyers, or something else less cheery, based on your Internet travels?
Privacy advocates and technology experts have long warned about the intrusiveness of invisible online tracking. In recent months, the Federal Trade Commission has been urging the industry to adopt more transparent practices and to offer consumers a simple way to opt out of online tracking if it bothers them.
The sword of Damocles hanging over the industry is the idea of a standardized "Do Not Track" option for Web browsers, akin to the national "Do Not Call" registry that helped tame unwanted telemarketing. In response, the industry has been promoting a "best-practices" approach while pushing forward with tools that make it easier for consumers to see how trackers work and to avoid the ads if they wish.
Will it work? Yes, is the prediction of Scott Meyer, founder and chief executive officer of Evidon Inc., a key player in the industry's efforts to clean up its own act. Meyer says consumers see most behavioral targeting as "benign and even beneficial. The issue isn't one of harm; it's an issue of transparency."
Outside the industry, many still voice doubts.
A key challenge with any self-regulation is how to deal with outliers - companies on the fringes that often cause the most problems.
"It's kind of like the Wild West," says Ashkan Soltani, a researcher, consultant, and former FTC technologist, who studied behavioral tracking as a graduate student at the University of California and whose research is posted at KnowPrivacy.org. "It's unlikely that industry groups will be able to corral them all."
What can Internet users do right now to gain a handle on tracking, or avoid it? Here are three possibilities:
Turn off third-party cookies. This is the most direct approach for blocking behavioral tracking, because third-party cookies are a key to how the systems usually work.
First-party cookies are the useful data files placed on your computer by a website when you visit. They're handy if you want a site to remember you - to save things like log-in information, a shopping cart, or a wish list.
Third-party cookies, typically placed on your computer by an ad network or data-gathering company, are another matter. Although turning them off may interrupt some functionality, such as your ability to play an embedded video or use a Facebook widget, Soltani says their main value is as a tracking tool.
You'll find controls for third-party cookies under the Tools menus of both Firefox and Internet Explorer.
To see what's going on, or to opt out. Evidon owns a tool called Ghostery, a browser extension available within Firefox or from http://ghostery.com/download for every major browser that enables you to see who's watching and tell them to stop. A similar tool, Abine, is available at www.abine.com.
With Ghostery, you'll see a bubblelike window on any Web page you visit that lists the source of "Web bugs" or "beacons" on the page. Those are the hidden codes on Web pages that find third-party cookies and allow advertisers to track you.
Just seeing the lists is an eye-opener. Some sites show evidence of tracking by dozens of companies. On Wednesday, the home page of Salon.com showed more than 20, and Philly.com listed more than a dozen.
Ghostery and Abine also offer opt-out options that allow you to reject tracking by some companies.
The "Advertising Option" icon. Look for this - a triangle standing on one corner, with an "i" in the middle for information. Also promoted for the industry by Evidon, it's a click-and-learn-more tool you'll soon see in online ads. Of course, to see the information, you'll have to click within the ad - a tough step for the ad-wary Internet user.
The industry's hope is that the more you know about its ads, the less you'll worry.
Contact columnist Jeff Gelles
at 215-854-2776 or firstname.lastname@example.org.