SAN FRANCISCO — Dozens of websites have been secretly harvesting lists of places that their users previously visited online, everything from news articles to bank sites to pornography, a team of computer scientists found.
The information is valuable for con artists to learn more about their targets and send them personalized attacks. It also allows e-commerce companies to adjust ads or prices — for instance, if the site knows you've just come from a competitor that is offering a lower price.
Although passwords aren't at risk, in harvesting a detailed list of where you've been online, sites can create thorough profiles on its users.
The technique the University of California, San Diego researchers investigated is called "history sniffing" and is a result of the way browsers interact with websites and record where they've been. A few lines of programming code are all a site needs to pull it off.
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Although security experts have known for nearly a decade that such snooping is possible, the latest findings offer some of the first public evidence of sites exploiting the problem. Current versions of the Firefox and Internet Explorer browsers still allow this, as do older versions of Chrome and Safari, the researchers said.
The report adds to growing worry about surreptitious surveillance by Internet companies and comes as federal regulators in the U.S. are proposing a "Do Not Track" tool that would prevent advertisers from following consumers around online to sell them more products.
The researchers found 46 sites, ranging from smutty to staid, that tried to pry loose their visitors' browsing histories using this technique. Nearly half of the 46 sites, including financial research site Morningstar.com and news site Newsmax.com, used an ad-targeting company, Interclick.
Interclick said the tracking was part of an eight-month experiment that the sites weren't aware of. It has stopped using the technique and emphasized that it didn't store the browser histories.
Morningstar said it ended its relationship with Interclick when it found out about the program; NewsMax said it is investigating.
The researchers studied far more sites and said many more behaved suspiciously, but couldn't be proven to use history sniffing.
"Browser vendors should have fixed this a long time ago," said Jeremiah Grossman, an Internet security expert at WhiteHat Security Inc.".. People really should upgrade their browsers."
The latest versions of Google Inc.' s Chrome and Apple Inc.' s Safari have automatic protections for this kind of snooping. Mozilla Corp. said the next version of Firefox will have the same feature, and a workaround exists for some older versions.
Microsoft Corp. noted that Internet Explorer users can enable a private browsing mode that prevents the browser from logging the user's history.