• Pop-up ads, which appear in a new browser window when you arrive at a Web page and block part of that page or all of that page (interstitials).
• Pop-under ads, which load in the background under the current page and appear when you close that page.
• Spawning results in multiple browser windows that open, one after another, when you enter or exit a site.
• Mouse trapping disables your ability to click back to a previous page or to use your mouse to exit your browser.
• Pop-up spam ads pop up on your screen if you’re connected to the Internet, regardless of whether you have your Web browser running.

Web advertisers are using these techniques in ever-greater numbers. Almost one out of three of the largest Web sites in the U.S. now use pop-up and pop-under ads, according to a survey by Cyveillance, an Internet services consulting firm. About 5 percent use mouse trapping. And 1.4 percent go so far as changing your home page or favorites list.

Many of these techniques were developed by programmers of adult Web sites, who have no shame. Some mainstream Web sites, having no shame, are now doing the same.

Web surfers are fighting back. Some are using ad-blocking software, sometimes called “ad killers.” These programs are widely available as inexpensive “shareware” or “freeware,” typically from individual entrepreneurs. Popular choices include AddSubtract and Guard-IE Popup Killer and Privacy Suite, available from download sites such as CNET’s Download.com, at http://www.download.com.

One program, Pop-Up Defender, uses a reviled form of marketing, e-mail spam, to try to persuade you to buy it in order to stop another reviled form of marketing, pop-up ads. Don’t be a sucker. EarthLink subscribers get the use of a pop-up blocking tool for free.

Ad-blocking software is beginning to become mainstream. For some time, utility powerhouse Symantec, at http://www.symantec.com, has bundled an ad-blocking component with its Norton Internet Security. More recently, Web browsers such as Mozilla, at http://www.mozilla.org, and the newly released Apple Safari, at http://www.apple.com/safari, have begun to offer this capability, preventing consumers from having to use a third-party tool.

You’d think advertisers would get the message. But reports indicate that some sites are upping the ante, resorting to technologies that disable all or part of their sites if they detect you’re using ad-blocking software.

Bad move, says Gary Stein, an analyst specializing in Internet marketing at Jupiter Research, a market research firm headquartered in New York City. “In a war between advertisers and consumers, consumers will win,” he says. “An angry consumer won’t be a customer.”

Recognizing that the Internet is all about freedom of choice, some enlightened Web publishers are adopting different strategies. America Online now bans third-party pop-up ads (but not its own). iVillage, at http://www.ivillage.com, bans all pop-ups. Salon.com, at http://www.salon.com, bans all ads if you subscribe ($30/year), or you can choose to view the site for free, including its pop-up and banner ads.

Some Web publishers will be tempted to use “integrated advertising” to make ad messages seem like regular content or “contextual advertising” to tailor ads to individuals by tracking their surfing habits.

Making ads more “relevant” in these ways, however, is a slippery slope, raising thorny ethical and privacy issues. Blurring the lines between editorial and advertising is deceitful unless sites clearly label the sponsored content, as print publications do with advertorials. And using “spyware” that tracks what you do online risks creating a huge consumer backlash. A better approach here is to ask surfers to voluntarily answer questions.

What advertisers need to do in general, says Stein, is what they’ve always done best: Be creative. Instead of hijacking consumers’ surfing time, create interesting ads with fun or substantive content that people want to see.