An HTTP cookie[2], also known as a web cookie or browser cookie, is a small piece of data stored on a user’s device by their web browser while they are browsing a website[3]. Cookies are designed to hold a modest amount of data specific to a particular client and website, and can be used to deliver a personalized web experience. They can remember information about a user’s visit, such as their preferred language and other settings. This makes subsequent visits easier and the site more useful. Cookies play a crucial role in facilitating online activities like online shopping and personalization[1] of web pages. They also help website owners understand how visitors interact with their sites, enabling them to improve the structure and content. Yet, some types of cookies can pose security[4] risks, so it’s important for users to be aware of them and know how to manage them.
HTTP cookies (also called web cookies, Internet cookies, browser cookies, or simply cookies) are small blocks of data created by a web server while a user is browsing a website and placed on the user's computer or other device by the user's web browser. Cookies are placed on the device used to access a website, and more than one cookie may be placed on a user's device during a session.
Cookies serve useful and sometimes essential functions on the web. They enable web servers to store stateful information (such as items added in the shopping cart in an online store) on the user's device or to track the user's browsing activity (including clicking particular buttons, logging in, or recording which pages were visited in the past). They can also be used to save information that the user previously entered into form fields, such as names, addresses, passwords, and payment card numbers for subsequent use.
Authentication cookies are commonly used by web servers to authenticate that a user is logged in, and with which account they are logged in. Without the cookie, users would need to authenticate themselves by logging in on each page containing sensitive information that they wish to access. The security of an authentication cookie generally depends on the security of the issuing website and the user's web browser, and on whether the cookie data is encrypted. Security vulnerabilities may allow a cookie's data to be read by an attacker, used to gain access to user data, or used to gain access (with the user's credentials) to the website to which the cookie belongs (see cross-site scripting and cross-site request forgery for examples).
Tracking cookies, and especially third-party tracking cookies, are commonly used as ways to compile long-term records of individuals' browsing histories — a potential privacy concern that prompted European and U.S. lawmakers to take action in 2011. European law requires that all websites targeting European Union member states gain "informed consent" from users before storing non-essential cookies on their device.