Pop-up blockers like Google's or Yahoo's don't prevent these ads from appearing because they use a different command.
Floating ads appear because they're written in coding language called dynamic HTML, which contains a series of embedded commands that ad blockers typically don't block.
Sites including Netscape and MSN Money use overlay advertisements in lieu of pop-ups.
Many ad-delivery companies are now using technology to detect whether or not a computer or visitor has installed a pop-up blocker. If one is detected, it will deliver a floating ad to the page instead. Burst Media, for example, is one company that is experimenting with the overlays.
"Instead of a pop, they float over the page," said Jarvis Coffin, chief executive of Burst Media, which represents ad sales for about 2,000 sites.
Undertone Networks, one of the largest distributors of pop-under ads, with customers including Yahoo Personals, HBO and Orbitz, uses pop-up blocking detection technology from Zedo, an ad delivery company based in San Francisco.
Yahoo spokeswoman Stephanie Iwamasa said that because the ads are delivered differently, the company doesn't necessarily consider them pop-ups and therefore doesn't block them. However, she said, Yahoo is always evaluating new technologies to help improve consumers' experience on the Web.
Pop-ups came into fashion during the dot-com bust, when publishers were desperate for ad dollars and sought to please marketers with more attention-grabbing means to reach consumers. But Web surfers came to loathe them, and publishers such as the Web site for The New York Times moved to regulate how often people receive them.
Downloadable software to block the ads also has become ubiquitous; major Internet service providers, software companies like Panicware, and even Amazon.com offer tools to staunch them.
Yet it remains to be seen whether they will die out now that the overall Internet advertising industry has rebounded. Last week, the trade group Interactive Advertising Bureau reported a record quarter of sales for the industry, the highest since it began tracking the sector in 1996. Sales for the first three months of 2004 were $2.3bn (£1.25bn), up from $1.6bn in the year-ago period.
Jason Krebs, head of online ad sales for The New York Times' Web site, said that the online newspaper continues to sell pop-unders as one of many options because they're effective for advertisers. He added that he has no problem with blocking technologies from Google and others.
"You cannot stop technologies. What we do is we adapt to the changing technologies (and advertising environment) and continue to operate the business successfully," Krebs said.
Talkback
If you have a lot of pop-ups, try this cure: Mozilla's Firefox.
Vote with your money, if a company uses pop-up/under ads, don't buy from them.
It just depends on how bad you want them to go away.
Agree with the above post. Use Mozilla Firefox.