Zombie Cookie


A zombie cookie is a type of tracking cookie in digital technology that recreates itself after being deleted by the user. It does this by storing its information in multiple locations on a system, such as Flash Local Shared Objects, and HTML5 storage. This allows the cookie to be extremely persistent and more invasive to user privacy compared to regular cookies.


The phonetics of the keyword “Zombie Cookie” is:/zɒmbiː kʊkiː/

Key Takeaways

  1. Zombie Cookies – These are a type of tracking cookie that automatically regenerates after being deleted. This makes them hard to remove and they can track user activity, often without the user’s knowledge or consent.
  2. Privacy Concerns – Due to their persistent nature and ability to track user’s online behavior, Zombie cookies raise significant privacy concerns. They are often used by advertisers and third-party tracking services to collect detailed user profiles.
  3. Prevention – Preventing Zombie cookies can be difficult, but using more privacy-focused web browsers, regularly clearing cookies and using ad-blocking or anti-tracking software can help in minimizing the risk.


The term “Zombie Cookie” is important in technology, specifically in internet privacy, as it refers to a type of persistent tracking cookie that can regenerate itself even after being deleted by the user. This is achieved by storing the cookie’s data in multiple locations, such as Adobe Flash Local Shared Object storage. Upon deletion, the cookie resurrects itself using the stored data, hence the term “zombie”. This technology is controversial because it infringes on the privacy of users, persistently tracking and gathering their information without their consent or knowledge. Therefore, understanding and managing zombie cookies becomes critical to maintaining user’s internet privacy and security.


Zombie cookies refer to HTTP cookies that are recreated after deletion, usually stored outside the web browser’s dedicated cookie storage area. This technology is used mainly for tracking purposes — enabling the persistent identification and tracking of users even after they have cleared their browser cookies. This tracking method often supports online ad serving processes, allowing for enhanced user-profile specific ad targeting. Essentially, zombie cookies are used by many marketers to gather valuable, granular demographic and psychographic user data, supporting more targeted and personalized advertising efforts.Furthermore, zombie cookies have the ability to auto-regenerate primarily because they don’t rely on the traditional browser cookie storage. Numerous storage mechanisms such as flash cookies and web storage in HTML5 can be used to achieve zombie cookies. It is pertinent to note that the use of such cookies comes under scrutiny due to privacy concerns, as these cookies can be resurrected without the knowledge or approval of the user, leading to potential unauthorized access of browsing history and information. Despite the privacy issues, its significant value to digital advertising as a tracking tool makes it widely employed in the industry.


1. “Quantcast” Case: In 2010, online advertising firm Quantcast was accused of using zombie cookies. The Federal Trade Commission charged them for recreating cookies that users had deleted, in order to continue tracking their web activity without their knowledge or consent. The case was settled out of court.2. “Hulu” Incident: This popular streaming video website was caught up in a scandal over zombie cookies in 2011. Wired Magazine reported that Hulu and its tracking company, KISSmetrics, were using a type of zombie cookie that regenerated even after users have tried to block or delete them. They faced a class-action lawsuit over the questionable practice.3. “Turn” Controversy: In 2015, ad company Turn used zombie cookies to track unknowing Verizon Wireless customers. The Electronic Frontier Foundation (EFF) and ProPublica revealed how Turn had been exploiting Verizon’s UIDH “supercookie” to resurrect deleted tracking cookies. This case also resulted in an out-of-court settlement.

Frequently Asked Questions(FAQ)

**Q: What is a Zombie Cookie?**A: A Zombie Cookie, in the technology realm, is a cookie that recreates itself after deletion from a backup stored online. The purpose is to keep user information intact even if the user deletes the cookie.**Q: How does a Zombie Cookie work?**A: Zombie Cookies function by persistently storing user information in multiple areas such as Flash storage, web history, and HTML5 storage. Even if the user deletes the primary cookie, a Zombie Cookie can regenerate from the stored data.**Q: Are there any privacy concerns with Zombie Cookies?**A: Yes, there are serious privacy concerns surrounding Zombie Cookies. They track and store user information persistently even if the user has expressly deleted cookies, which can be against privacy protocols.**Q: Can you prevent Zombie Cookies?**A: It can be challenging to fully prevent Zombie Cookies, but steps can be taken to minimize them. Several methods include disabling Flash storage, using private browsing modes, or using anti-tracking software.**Q: Is it legal to use Zombie Cookies?**A: Zombie Cookies can land in a grey area when it comes to legality. While they’re not outright illegal in all places, they do often contravene privacy laws, regulations, and standards established by different nations and organizations.**Q: How can I detect Zombie Cookies?**A: Detecting Zombie Cookies can be a quite technical process as they are created to be hidden. Using a cookie detector tool or manually inspecting cookies through your browser settings can help identify them.**Q: Why are they called “Zombie Cookies”?**A: They are named “Zombie Cookies” due to their ability to come back to life after being deleted, similar to a zombie in popular culture. They return from the “dead” by recreating themselves from backup data.

Related Tech Terms

  • HTTP Cookies: A small amount of data stored on the user’s computer by the web browser while browsing a website. They are a foundation technology for zombie cookies.
  • Evercookie: A javascript API that produces extremely persistent cookies in a browser. It is a way to create a zombie cookie.
  • Web Storage: This is a web application software method used for storing data in a web browser. Zombie cookies can exploit web storage mechanisms.
  • Flash Cookies: Also known as Local Shared Objects, these are pieces of data that websites which use Adobe Flash may store on a user’s computer. Zombie cookies can regenerate from these flash cookies.
  • Privacy Invasion: This term refers to the violation of an individual’s privacy. Zombie cookies are often viewed as a method of privacy invasion as they can reappear even after deletion.

Sources for More Information


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