Feeds

Man reveals secret recipe behind undeletable cookies

New and improved cookie 'respawning' revealed

Security for virtualized datacentres

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. ®

Secure remote control for conventional and virtual desktops

More from The Register

next story
NASTY SSL 3.0 vuln to be revealed soon – sources (Update: It's POODLE)
So nasty no one's even whispering until patch is out
Russian hackers exploit 'Sandworm' bug 'to spy on NATO, EU PCs'
Fix imminent from Microsoft for Vista, Server 2008, other stuff
'LulzSec leader Aush0k' found to be naughty boy not worthy of jail
15 months home detention leaves egg on feds' faces as they grab for more power
Forget passwords, let's use SELFIES, says Obama's cyber tsar
Michael Daniel wants to kill passwords dead
FBI boss: We don't want a backdoor, we want the front door to phones
Claims it's what the Founding Fathers would have wanted – catching killers and pedos
Kill off SSL 3.0 NOW: HTTPS savaged by vicious POODLE
Pull it out ASAP, it is SWISS CHEESE
Facebook slurps 'paste sites' for STOLEN passwords, sprinkles on hash and salt
Zuck's ad empire DOESN'T see details in plain text. Phew!
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Why cloud backup?
Combining the latest advancements in disk-based backup with secure, integrated, cloud technologies offer organizations fast and assured recovery of their critical enterprise data.
Win a year’s supply of chocolate
There is no techie angle to this competition so we're not going to pretend there is, but everyone loves chocolate so who cares.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Intelligent flash storage arrays
Tegile Intelligent Storage Arrays with IntelliFlash helps IT boost storage utilization and effciency while delivering unmatched storage savings and performance.