Flash Cookies and Privacy II: Now with HTML5 and ETag Respawning

In August 2009, the authors 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. The authors 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, the authors reassess the Flash cookies landscape and examine a new tracking vector, HTML5 local storage and Cache-Cookies via ETags.