Marketer taps browser flaw to see if you're pregnant

A gaffe of Epic proportions

A prominent online marketer that helps websites deliver targeted ads has been exploiting a decade-old browser flaw that leaks the history of websites that users visit, a researcher from Stanford University reported.

Epic Marketplace doesn't use the well-documented browser history leak to track specific websites a user has clicked on, Stanford graduate student Jonathan Mayer said. But it does employ advanced code that tests thousands of visited links per second to compile visitors' interests, including home improvement, pregnancy and fertility, and the repair of bad credit, he said.

Mayer's findings are based on Epic-supplied JavaScript found on websites for online movie service Flixter and cable and internet service provider Charter.net. The code, he said, works behind the scenes and is able to process thousands of URLs per second. If a user exits the browser or visits a new site before the script is done, a browser cookie stores the progress so the search may be resumed at a later time.

The report comes eight months after researchers from the University of California at San Diego caught YouPorn.com and 45 other sites pilfering visitors' surfing habits, including whether they had recently browsed to PornHub.com and other smut sites. The operator of YouPorn and Interclick, one of the ad-serving companies exposed by the researchers, have since been sued over the practice.

Until recently, a privacy weakness built into virtually every browser made it trivial for websites to compile detailed lists of websites viewed by their visitors. The sniffing technique worked by analyzing the color of links browsers use to show which URLs a user has already clicked on. Mozilla Firefox was the first major browser to plug the leak. All other major browser makers have since followed suit.

About half the world's browser users remain vulnerable to history sniffing because they haven't upgraded to a fixed version, Mayer said.

An Epic Marketplace spokesman said in an email: "The company compiles broad interest segments, but not related to sensitive categories or sites." He didn't respond to a follow up question asking if interests such as pregnancy and bad credit were tracked. Epic has also posted a response to Mayer's report here.

This article was updated to correct information about Internet Explorer.

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