How Technologies Aggregate User Browsing History Across Multiple Sites: Methods, Risks, and Privacy Solutions

By Christopher TaylorLast Updated July 31, 2025

Introduction

In today’s interconnected digital ecosystem, companies strive to understand users by collecting data about online activity across multiple websites. This practice, known as cross-site tracking , enables businesses to aggregate browsing history and construct comprehensive user profiles. While this facilitates highly personalized experiences and targeted advertising, it also raises profound privacy concerns and spurs ongoing technological innovation in both tracking and privacy protection. [2]

How Companies Aggregate Browsing History Across Multiple Sites

To aggregate a user’s browsing history, organizations rely on a mix of technologies. Historically, third-party cookies have been the most prevalent method. When you visit a site, a tiny file-a cookie-is placed in your browser. If the same company operates on other websites you visit, the cookie acts as a persistent identifier, allowing that company to track you across its network of sites. [5]

For example, after shopping for a Hello Kitty gift on Amazon, you might see Hello Kitty ads on numerous unrelated sites. This is because your browsing history and interests have been aggregated using cross-site tracking technologies. [5]

Key Technologies Used

Beyond cookies, companies use several advanced solutions:

Scripts and Tags: JavaScript snippets embedded in web pages can send data about your activity to central servers. [2]
Shared Storage and Private Aggregation APIs: Newer approaches, such as the Shared Storage API and Private Aggregation API, enable companies like Ogury to collect cross-site data without relying on traditional tracking, thus enhancing privacy while still aggregating user activity. [1]
Fingerprinting: Techniques that collect details about your browser and device configuration to create a unique identifier, bypassing cookie restrictions.

Case Study: Ogury’s Use of Shared Storage and Private Aggregation APIs

Ogury, a leader in digital advertising, leverages the Shared Storage API to store user survey responses directly in the browser. When users later see Ogury ads on other sites, the browser sends site domain and stored responses to the Private Aggregation API . This API decodes and aggregates the results, enabling cross-site data collection while avoiding traditional cookies. [1]

Ogury’s tests demonstrated that these privacy-preserving APIs could still deliver valuable business insights without exposing sensitive user data. This approach exemplifies the transition toward technologies balancing utility and user privacy.

Applications and Benefits

Aggregating browsing history provides several business advantages:

Personalization: Companies can customize website content and recommendations based on aggregated user interests.
Targeted Advertising: By understanding browsing patterns, advertisers display relevant ads, improving engagement and ROI. [5]
Analytics and Optimization: Businesses analyze aggregated data to improve website UX and identify valuable content. [2]

Real-World Example

When a user searches for products on one retail site and later visits blogs, news outlets, or social networks, cross-site tracking enables the aggregation of these actions. As a result, product ads reappear on unrelated sites, reflecting the user’s prior interests.

Privacy Risks and Challenges

While aggregating browsing history can enhance the user experience, it also introduces significant privacy risks:

Loss of Anonymity: Persistent identifiers can reveal extensive details about a user’s habits and interests.
Data Leakage: Improper handling of cross-site data can expose sensitive information to unintended parties. [4]
Manipulation and Exploitation: Attacks such as Cross-Site History Manipulation (XSHM) exploit browser history partitioning flaws, leading to privacy violations, login status detection, and resource mapping. [4]

Research shows that about 80% of users value website personalization, but many are unaware of the extent to which their data is collected and aggregated across sites. [5]

Potential Challenges

Companies must navigate several hurdles:

Compliance with privacy regulations such as GDPR and CCPA.
Maintaining user trust while leveraging aggregated data.
Ensuring that aggregation technologies do not introduce new security vulnerabilities.

Controlling and Preventing Cross-Site Tracking

Recognizing privacy risks, browser vendors have introduced features to block or limit cross-site tracking:

Google Chrome: Users can block third-party cookies by navigating to
Settings > Privacy and security > Cookies and other site data
, then enabling
Block third-party cookies
. [3]
Mozilla Firefox: Features
Enhanced Tracking Protection
enabled by default. Access via
Settings > Privacy & Security > Enhanced Tracking Protection
. [3]
Apple Safari: Built-in tracking prevention can be activated in
Settings (Preferences) > Privacy > Prevent cross-site tracking
. [3]

These features empower users to limit how much of their browsing history is aggregated by companies across multiple sites.

Step-by-Step Guidance for Users

If you wish to minimize cross-site tracking and aggregation of your browsing history, follow these steps:

Review Browser Settings: Access your browser’s privacy settings and enable options to block third-party cookies or cross-site tracking.
Use Privacy-Focused Browsers: Consider browsers that prioritize privacy by default, such as Firefox or Brave.
Install Privacy Extensions: Tools like Privacy Badger or uBlock Origin can further limit cross-site tracking.
Regularly Clear Cookies: Removing cookies can disrupt persistent tracking, although this may affect site functionality.
Understand and Manage Permissions: Be cautious about granting permissions to third-party scripts and trackers.

As privacy technology evolves, companies are adopting new standards that balance business needs with user protection. APIs like Shared Storage and Private Aggregation offer promising alternatives to legacy tracking methods.

Alternative Approaches and Industry Trends

With privacy regulations tightening and browsers restricting traditional tracking, several alternative methods have emerged:

Contextual Advertising: Instead of relying on user history, ads are displayed based on current content or context.
First-Party Data Aggregation: Companies aggregate data only from sites they directly own or operate, reducing third-party risks.
Privacy-Preserving Aggregation: Technologies such as Private Aggregation API aggregate data in ways that prevent individual user identification. [1]

These trends reflect a shift toward responsible data practices, supporting both business goals and user privacy.

Actionable Steps for Companies

For organizations seeking to aggregate user browsing history across multiple sites, consider the following:

Choose technologies that comply with privacy laws and industry best practices.
Evaluate privacy-preserving APIs like Shared Storage and Private Aggregation for cross-site insights.
Be transparent with users: Clearly disclose data practices and offer opt-out options.
Regularly audit tracking infrastructure to ensure user data is not exposed or misused.
Monitor regulatory changes and adapt strategies accordingly.

For specific implementation, consult official browser documentation and privacy standards organizations. When in doubt, search for terms like “cross-site tracking prevention” or “privacy-preserving aggregation” on reputable industry portals.

Conclusion

Technologies that enable companies to aggregate user browsing history across multiple sites are evolving rapidly, balancing personalization and privacy. Companies employ cookies, scripts, and advanced APIs to gain insights, while users and regulators push for stronger privacy controls. By understanding these mechanisms and applying best practices, both businesses and individuals can navigate the future of web tracking responsibly.