January 24, 2022

New Follow-Up Study: "Flash Cookies and Privacy II: Now with HTML5 and ETag Respawning"

Follow Up Study:
“Flash Cookies and Privacy II: Now with HTML5 and ETag Respawning”


Mika Ayenson, Worcester Polytechnic Institute (WPI)

Dietrich James Wambach, University of Wyoming

Ashkan Soltani, University of California, Berkeley – School of Information

Nathan Good, Good Research

Chris Jay Hoofnagle, University of California, Berkeley – School of Law, Berkeley Center for Law & Technology

In August 2009, we demonstrated that popular websites were using “Flash cookies” to track users. Some advertisers had adopted this technology because it allowed persistent tracking even where users had taken steps to avoid web profiling. We also demonstrated “respawning” on top sites with Flash technology. This allowed sites to reinstantiate HTTP cookies deleted by a user, making tracking more resistant to users’ privacy-seeking behaviors.

In this followup study, we reassess the Flash cookies landscape and examine a new tracking vector, HTML5 local storage and Cache-Cookies via ETags.

We found over 5,600 standard HTTP cookies on popular sites, over 4,900 were from third parties. Google-controlled cookies were present on 97 of the top 100 sites, including popular government websites. Seventeen sites were using HTML5, and seven of those sites had HTML5 local storage and HTTP cookies with matching values. Flash cookies were present on 37 of the top 100 sites.

We found two sites that were respawning cookies, including one site – hulu.com – where both Flash and cache cookies were employed to make identifiers more persistent. The cache cookie method used ETags, and is capable of unique tracking even where all cookies are blocked by the user and “Private Browsing Mode” is enabled.

Additional Info and Download (Free) Full Text Study via SSRN

See Also: 2009 Study (via SSRN)

About Gary Price

Gary Price (gprice@mediasourceinc.com) is a librarian, writer, consultant, and frequent conference speaker based in the Washington D.C. metro area. Before launching INFOdocket, Price and Shirl Kennedy were the founders and senior editors at ResourceShelf and DocuTicker for 10 years. From 2006-2009 he was Director of Online Information Services at Ask.com, and is currently a contributing editor at Search Engine Land.