Feeds

Man reveals secret recipe behind undeletable cookies

New and improved cookie 'respawning' revealed

The Essential Guide to IT Transformation

A privacy researcher has revealed the evil genius behind a for-profit web analytics service capable of following users across more than 500 sites, even when all cookie storage was disabled and sites were viewed using a browser's privacy mode.

The technique, which worked with sites including Hulu, Spotify and GigaOm, is controversial because it allowed analytics startup KISSmetrics to construct detailed browsing histories even when users went through considerable trouble to prevent tracking of the websites they viewed. It had the ability to resurrect cookies that were deleted, and could also compile a user's browsing history across two or more different browsers. It came to light only after academic researchers published a paper late last month.

KISSmetrics CEO responded with a post on its website claiming the research “significantly distorts our technology and business practices.” The company also responded by adding a “consumer-level opt-out for those who wish to be entirely removed from all KISSmetrics tracking, going well beyond the options that other analytics companies provide.”

Ashkan Soltani, one of the researchers, stands by the findings and said KISSmetrics' recently updated privacy policy doesn't make it clear how users go about opting out of tracking.

At the heart of the technique is the practice of storing a unique identifier, known as an ETag value, in a browser's cache and metadata folders. A piece of JavaScript hosted on kissmetrics.com accesses the serial number each time one of the KISSmetrics websites is viewed.

“It's effectively acting like a cookie because with every connection to KISSmetrics, it will send a referrer header and the ETag value,” Soltani told The Register. “The ETag is effectively acting as a cookie. It has the same exact value of the cookie as well.”

KISSmetrics analytics combined the the ETag technique with several other controversial technologies that use cookies based on Adobe Flash and HTML5 to reproduce tracking cookies even after a user had specifically deleted them. Soltani and his colleagues first documented the sneaky move in 2009 and dubbed it cookie “respawning.”

Adobe responded by building an application interface that made it easy for users to delete Flash cookies using standard features in a browser's menu. The advent of server-based scripts that pull up ETag data means that it's once again trivial for analytics services to defy the wishes of visitors who don't want to be tracked.

“The more accurately they can represent the number of uniques that have visited their sites the more value they can provide for their analytics customers,” Soltani explained. “That might mean you as a person who doesn't want to be tracked uniquely trying to opt out. They're incentivized to circumvent that opt-out.”

Soltani said the only way to block the tracking using the technique is to block all cookies and to clear the browser cache after each site visited. He has published a detailed technical description of the new technique here. ®

Build a business case: developing custom apps

More from The Register

next story
14 antivirus apps found to have security problems
Vendors just don't care, says researcher, after finding basic boo-boos in security software
Secure microkernel that uses maths to be 'bug free' goes open source
Hacker-repelling, drone-protecting code will soon be yours to tweak as you see fit
Only '3% of web servers in top corps' fully fixed after Heartbleed snafu
Just slapping a patched OpenSSL on a machine ain't going to cut it, we're told
How long is too long to wait for a security fix?
Synology finally patches OpenSSL bugs in Trevor's NAS
Israel's Iron Dome missile tech stolen by Chinese hackers
Corporate raiders Comment Crew fingered for attacks
Roll out the welcome mat to hackers and crackers
Security chap pens guide to bug bounty programs that won't fail like Yahoo!'s
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
Researcher sat on critical IE bugs for THREE YEARS
VUPEN waited for Pwn2Own cash while IE's sandbox leaked
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.