Zombie Cookies

Implementation

According to TRUSTe: “You can get valuable marketing insight by tracking individual users’ movements on your site. But you must disclose your use of all personally identifiable information in order to comply with the Fair Information Practices guidelines.”[3]. The following storage mechanisms are available:

• Standard HTTP Cookies

• Storing cookies in and reading out Web History

• Storing cookies in HTTP ETags

• Internet Explorer userData storage   (starting IE9, userData is no longer supported)

• HTML5 Session Storage

• HTML5 Local Storage

• HTML5 Global Storage

• HTML5 Database Storage via SQLite

• Storing cookies in RGB values of auto-generated, force-cached PNGs using HTML5 Canvas tag to read pixels (cookies) back out

• Local Shared Objects (Flash Cookies)

• Silverlight Isolated Storage

If a user is not able to remove the cookie from every one of these data stores then the cookie will be recreated to all of these stores on the next visit to the site that uses that particular cookie. Every company has their own implementation of zombie cookies and those are kept proprietary. An open-source implementation of zombie cookies, called Evercookie [4], is available. This is an educational example that is intended to show the numerous possible places for zombie cookies to be hidden.

Removal of Zombies

Zombies would not seem that eerie and dreadful if you knew where they come from and how to eradicate them at their origins.

For zombie cookies, the eradications can be summarized as below:

• Delete browser cookies

  • IE Tools --> Delete Browsing History... --> Cookie

  • Firefox Tools --> Clear Recent History... --> Cookies

  • Chrome Tools --> Clear Browsing Data --> Delete Cookies and other site data

• Clear browser cache

  • IE Tools --> Delete Browsing History... --> Temporary Internet files

  • Firefox Tools --> Clear Recent History... --> Cache

  • Chrome Tools --> Clear Browsing Data --> Empty the cache

• Clear browsing history

  • IE Tools --> Delete Browsing History... --> History

  • Firefox Tools --> Clear Recent History... --> Browsing & Download History

  • Chrome Tools --> Clear Browsing Data --> Clear browsing history

• Delete Flash Cookies

With your browser, go to Macromedia website storage settings panel and select listed websites that are tracking you via flash cookies and click delete button.

Below table lists all the data stores used by zombie cookies, and methods of deletions on various browsers.

Most of the modern browsers offer private browsing mode, namely Chrome Incognito,[5] Firefox Private Browsing,[6] IE InPrivate Browsing.[7] In these modes, Flash cookie could not be used. When a user closes his browser, the browser cache and cookies are deleted automatically, that clears out most of the backup stores for zombie cookie, though browsing history seems persist, that leaves a door open for zombies to come back.