It may have happened to you that after reading a news article or checking the price of a product, you leave a website and visit it again a few hours or days later. In this case the site may still display the chosen language, settings, items in the shopping cart, or even content similar to what you previously viewed.
At first glance, it seems the website remembered you; but behind this feature is a set of technologies that allow sites and online services to link a new visit to information about previous visits.
This identification is not necessarily done by a single method. The browser type, privacy settings, login status, and the technologies used by the site can play a role in how the user is re-identified.
Cookies; the simplest way to remember a user
Cookies are one of the most common technologies that websites use to remember users.
When a user visits a site, the website can store a small file in the browser containing identifiers or information needed to link the current visit to previous visits.
This information can be used to maintain login status, keep items in the shopping cart, or store user settings and preferences, such as the chosen language.
However, not all cookies serve the same purpose. Some cookies are essential for the proper functioning of the site, while others may be used for analyzing user behavior, advertising, or content personalization.
Logging in makes identification easier
When a user logs into their account, identifying them becomes much easier for the service. In this case, activities performed can be directly associated with that account.
Thus, the site can retrieve settings, preferences, and some information about previous activities when the user returns.
One advantage of this method is that user information is not necessarily limited to a specific device or browser. If a service syncs the relevant information with the user account, the user may be able to access their previous settings and data after logging into the same account on another device or browser.
Local storage; information that remains in the browser
Cookies are not the only tool for storing information in the browser. Modern browsers also provide technologies like Local Storage to websites.
Sites can use this capability to store various information such as settings, the state of certain features, or data that helps improve the user experience.
As a result, even when stored information is not directly visible while browsing the site, it may be used on the next visit to reconstruct part of the user's previous experience.
How does browser fingerprinting work?
A more complex method is called browser fingerprinting. In this method, the service can examine a set of technical characteristics of the device and the user environment; things like browser type, some software settings, screen size, and other technical features.
Each of these pieces of information alone is not necessarily sufficient to identify an individual. However, combining many of these signals can help a service distinguish between different users or devices.
Of course, the success of this method depends on the browser type, user settings, and anti-tracking tools, and different browsers and privacy technologies can limit such tracking.
Does your IP address identify you?
The IP address is also information provided to services when connecting to the internet, but it cannot by itself be equated with a person's identity.
An IP address may change, and multiple people or devices may use the same public address. For example, different devices in a home usually access the internet through a shared connection.
For this reason, websites typically combine a range of signals and different pieces of information rather than relying solely on IP to identify users.
How can online tracking be reduced?
Users can check their browser privacy settings and, if needed, clear cookies and site-stored data to reduce tracking. Using anti-tracking features and tools and blocking unnecessary permissions can also reduce the amount of information sites receive.
Private or incognito browsing mode can also limit some types of local storage, but it does not mean complete anonymity. This mode does not necessarily hide the user from websites or the internet service provider.
In the end, when a website "remembers" a user after they return, it does not necessarily mean the site knows their real identity. In many cases, the site only links the new visit to an identifier, data stored in the browser, an account, or a set of technical signals related to previous visits.