After a year of research, one firm thinks it knows. Leading Web Advertisers, an online ad measurement firm in New York, says one of its programmers has finally cracked the code to track AOL's "clickable" ads, such as banners, buttons and pop-up windows, which have long been hidden by a proprietary computer code AOL uses to create its pages.

Ever since advertising emerged as the Web's single largest source of revenue, advertisers have longed to know what their competitors are up to online. The problem: How to trace the thousands of ads displayed across millions of Web pages every day? While several well-established agencies collect data about TV and magazine ads, until the last few years there has been a dearth of focused information about Web ads.

Of particular interest has been who's running what ads and how often on AOL, the behemoth of Internet service providers. In September, 76 per cent of Web surfers visited AOL or one of its proprietary sites, according to Internet measurement firm Jupiter Media Metrix, which also estimates 40 per cent of US households online use AOL.

"AOL is probably the single most important media element in terms of online audience activity and its position to influence the marketplace in the future," says Ms Lynn Bolger, a managing director with media buying firm Initiative Media, a unit of Interpublic Group of Companies Inc. "This is a fundamental piece of information that's been missing."

Leading Web Advertisers, which says it now has the ability to monitor advertising on AOL, is one of several independent companies, including AdRelevance in Seattle, which are staking out a business monitoring where and when ads run on the Internet. Their clients use the collected data to hone ad campaigns and make sales targeting and prospecting more efficient. Leading Web Advertisers' 90-plus client list includes everyone from CNN to some online units of Omnicom Inc., as well as online ad servers DoubleClick Inc. and 24/7 Media Inc. The company plans to begin offering its AOL information this week.

"Everybody asks for it," says Leading Web Advertisers co-chief executive Mr Michael Kubin, who estimates 30 per cent of all ad dollars on the Web are spent on AOL or an AOL proprietary site. He compares not having information about AOL's advertisers to a world census that doesn't include China and India. Mr Kubin believes his company is the only one with the AOL data.

Although AOL is a client of Leading Web Advertisers, AOL says it believes Leading Web Advertisers' initial research on AOL is incomplete. Moreover, AOL says it has concerns about third-party trackers in general. "We don't want to make (tracking) difficult, what we want is for it to be correct and accurate and valid and we're not convinced that the work is being done correctly," says Mr Marshall Cohen, AOL's senior vice-president of brand development.

Nevertheless, advertisers are eager for any information they can get about AOL. By accessing a competitor's campaign from start to finish, marketers from consumer-product companies to drug companies to online brokerage houses can compare several key points, including how long the campaign ran, how often it changed creative content and what demographic group was targeted. The marketers can then adjust their own campaigns. Mr Kubin says Leading Web Advertisers captures at least 90 per cent of clickable online ads on the sites it tracks.

For AOL competitors, such as Yahoo! Inc. and Microsoft Corp.'s MSN, one key advantage to knowing who's advertising on AOL would be the ability to approach the advertisers, particularly ones who may be unclear on where best to advertise, and then offer a different mix of placement, possibly at a better price. How did AOL keep everything secret for so long? On most Websites, everything including ads, is written in a computer code called hypertext mark-up language (HTML). Ads have their own special code, which makes them easily identifiable. But AOL's sites predominantly are written in a code called Rainman. A Leading Web Advertisers programmer developed a code that could read Rainman and search for the ad markers.

AOL didn't specifically intend for Rainman to prevent an outsider from monitoring its sites, says AOL's Mr Cohen. AOL's system was developed 15 years ago, he says, before HTML became the industry standard. The company has stuck with it because it allows AOL to design pages that subscribers find easier and more intuitive to use, he says. Leading Web Advertisers considers its new AOL information such a boon to advertisers that it will charge an additional $1,000 or so a month for it. The two-year-old company already charges a monthly licensing fee of $2,000 for information it gathers on 2,250 Websites, including stats about some 40,000 brands and 300,000 ads.

Still, there remain holes in Leading Web Advertisers' information about AOL. The company still hasn't figured out how to find sponsorships and co-branded sites on AOL, which comprise a substantial portion of AOL's ad revenue, particularly from its old-line, brick-and-mortar advertisers. In fact, sponsorship pages aren't readily identifiable even in HTML because the Web pages where they appear aren't coded to reflect that they include those forms of advertising.

The Wall Street Journal