Cookie Respawning

Definition of Cookie Respawning

Cookie respawning is the practice of recreating a deleted HTTP cookie using stored backup data, often without the user’s knowledge or consent. It circumvents the user’s privacy choices and preferences by persisting tracking data even after cookies have been cleared. This technique is employed by some websites and third-party advertisers to track users’ browsing habits and serve targeted ads.


The phonetic pronunciation of “Cookie Respawning” is:Kookie – /ˈkʊki/ Re-spawning – /riˈspɔnɪŋ/

Key Takeaways

  1. Cookie Respawning is a technique used by websites to recreate deleted cookies, allowing them to continue tracking users even after they have cleared their cookies.
  2. It exploits various storage methods such as Flash Local Shared Objects (LSOs), HTML5 Local Storage, and other client-side storage techniques to store backup copies of tracking data.
  3. Users can protect themselves from Cookie Respawning by employing privacy-enhancing tools like browser extensions and regularly clearing all types of browser storage to help prevent persistent online tracking.

Importance of Cookie Respawning

Cookie respawning is an important technology term as it is related to the practice of recreating deleted cookies to ensure persistent tracking of user behavior and preferences across the internet.

This is crucial for both advertisers and websites, as it enables them to gain valuable insights into user preferences and behaviors, enhance their targeting capabilities, and improve online experiences.

However, cookie respawning is also controversial due to privacy concerns, as it can undermine user preferences and choices related to privacy, such as deleting cookies.

It highlights the ongoing debate between the importance of personalized online experiences and the protection of user privacy in the digital landscape.


Cookie respawning, commonly referred to as “evercookie” or “zombie cookie,” is a technique employed by some websites to maintain persistent user identification and tracking even after users have deleted their browser’s cookies. The primary purpose of cookie respawning is to enable website owners, advertising networks, and online platforms to obtain a more comprehensive understanding of user behavior, preferences, and the effectiveness of their online marketing campaigns.

This is achieved by continually recreating cookies that were manually deleted by users, effectively ensuring a continuous flow of information regarding user engagement and online habits. The underlying technology supporting cookie respawning is built using various storage mechanisms, such as Flash cookies, HTML5 Web Storage, and others, which permit the regeneration of deleted browser cookies.

When a user visits a website employing this technique, the site implements redundant sets of data across multiple storage channels which, when combined, recreates a user’s cookies even after they have been removed. Although cookie respawning may seem an invasion of privacy for some users, the information gathered through this method can enable website owners to optimize their digital content and advertising strategies, targeting audiences with increased precision and relevance.

Examples of Cookie Respawning

Cookie respawning is a technique used to recreate deleted cookies, allowing websites and third-party advertisers to continue tracking a user’s browsing activities even after they have cleared their cookies. Here are three real world examples:

Adobe Flash Local Shared Objects (LSO): Adobe Flash used to store Local Shared Objects (LSOs), also known as Flash cookies, that had the ability to respawn HTTP cookies. These Flash cookies could be used to store and retrieve data on the user’s system, allowing for a permanent identifier (known as an “evercookie”) that would persist even after the user had deleted regular cookies. This technique was widely used by digital advertisers and websites to track users across the web, despite their privacy efforts. However, with the discontinuation of Adobe Flash, LSO-based respawning is less prevalent now.

HTML5 Local Storage: HTML5 introduced a more powerful storage mechanism called local storage or Web Storage, which can be used by websites to store data on users’ browsers. Some websites have taken advantage of this technology to recreate deleted cookies. For example, a user might remove a tracking cookie from their browser, but the website could use local storage data to recreate the cookie next time the user visits, effectively respawning the tracking cookie.

Evercookies and Zombie Cookies: Evercookies are a more sophisticated form of tracking that use multiple storage methods, such as HTML5 local storage, Flash cookies, and ETag caching headers, to create unique identifiers for tracking users. Even if a user deletes their regular cookies, evercookies can use these alternative storage methods to respawn the cookie data. One infamous example is the use of “zombie cookies” by ad tech companies like Quantcast and Clearspring. They used cookie respawning to continued tracking users even after they had deleted their HTTP cookies, leading to lawsuits on grounds of privacy invasion.

FAQ – Cookie Respawning

What is cookie respawning?

Cookie respawning is a technique used by websites to recreate deleted cookies, often without the user’s knowledge. It involves storing the same information in multiple places (such as Flash cookies or HTML5 local storage) and using this information to recreate the standard HTTP cookies if they are deleted by the user.

Why do websites use cookie respawning?

Websites may use cookie respawning to track user behavior, gain valuable insights, target ads, or perform analytics. This can help them optimize website performance and user experience. However, some websites might use this practice without ensuring user consent, which can raise privacy concerns.

How can I prevent cookie respawning?

To prevent cookie respawning, you can regularly clear your browser’s cookies, cache, and local storage. Utilize browser extensions or settings designed to block or limit third-party cookies and restrict websites from accessing local storage. Regularly updating your browser to ensure that they have the latest security features can also help prevent cookie respawning.

Is cookie respawning illegal?

Cookie respawning is not explicitly illegal. However, it may violate privacy regulations in some jurisdictions if it is implemented without proper user consent or disclosure. For example, under the GDPR (General Data Protection Regulation) in the European Union, websites are required to obtain user consent before tracking cookies or similar technologies are placed on their devices.

How can I identify if a website is using cookie respawning?

Identifying cookie respawning can be challenging, as websites can use various methods to recreate cookies. You can inspect cookies and local storage in your browser’s developer tools or use browser extensions designed to monitor and analyze cookie behavior. Regularly clearing cookies and observing if they return can be another way to identify cookie respawning.

Related Technology Terms

  • HTTP Cookies
  • LocalStorage
  • Evercookie
  • Flash Cookies (LSOs)
  • Browser Fingerprinting

Sources for More Information


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