Quick definition: An evercookie is an extremely persistent JavaScript-based tracking tool that stores data in multiple browser locations. It can automatically regenerate, or “respawn,” itself even after a user attempts to delete standard cookies.
Explanation
An evercookie is a highly persistent tracking mechanism designed to resist deletion by storing redundant copies of its data across multiple browser storage locations. Developed by Samy Kamkar in 2010, it is not a traditional cookie but a JavaScript API that utilizes various storage systems such as HTML5 local storage, Flash Local Shared Objects, and cached image data. When a user deletes their standard browser cookies, the evercookie identifies the missing data and uses the remaining hidden copies to “respawn” or recreate the deleted files. This self-healing behavior ensures that a user can be consistently identified even after clearing their browser history or cache.
A common misconception is that evercookies are a form of malware; in reality, they are a tracking technology used primarily for persistent user identification and fraud prevention. Another myth is that clearing standard browser cookies provides complete privacy. Because evercookies hide in obscure locations like the RGB values of cached images, they often bypass standard privacy settings, requiring specialized tools or advanced browser configurations to remove completely.
Why it matters
- – Helps maintain your personalized settings and login status even if you accidentally clear your browser’s standard cookie cache
- – Ensures a smoother shopping experience by preventing your online cart items from being lost during unexpected connection drops or session resets
- – Protects your account security by helping websites recognize your trusted devices and detect potential unauthorized login attempts from new locations
How to check or fix
- – Clear all browsing history and website data simultaneously to remove identifiers stored in the standard cache and history logs
- – Manually delete local storage and session data within your browser settings to eliminate common alternative storage locations
- – Empty the browser’s image and favicon cache to remove identifiers hidden within cached media files
- – Reset or clear data for browser plugins and multimedia frameworks that maintain their own independent storage systems
- – Use private or incognito browsing modes to ensure that any persistent identifiers are automatically discarded once the session ends
- – Regularly update your browser to benefit from modern security features designed to isolate site data and prevent cross-site tracking techniques
Related terms
Zombie Cookie, Supercookie, Browser Fingerprinting, Tracking Cookie, Flash Cookie, HTML5 Storage
FAQ
Q: What is an evercookie?
A: An evercookie is an extremely persistent JavaScript-based tracking tool designed to identify a user’s browser even after standard cookies have been deleted. It works by storing redundant copies of data in multiple hidden storage locations across the device.
Q: Why are evercookies called “zombie cookies”?
A: They are called zombie cookies because of their ability to “respawn” or recreate themselves. If a user deletes the primary cookie but misses a copy hidden in another storage area, the evercookie will use that remaining data to restore itself in all other locations.
Q: How can I protect my privacy from evercookies?
A: Traditional “clear cookies” functions are often ineffective, so the best protection is using a browser’s private or incognito mode, which typically prevents these files from persisting after the session ends. You can also use advanced privacy tools like uBlock Origin or disable JavaScript on untrusted sites to block the tracking scripts.