Website cookies are small blocks of data created by a web server while a user is browsing a website and placed on the users computer or other device by the users web browser. Cookies are used to identify your computer to the network and are stored in a cookie file that’s placed in your browser’s folder on your hard drive. The next time you visit the same website, the browser will give back the cookie to identify you, and the website loads with a personalized experience.

Cookies serve useful and sometimes essential functions on the web. They enable web servers to store stateful information on the users device or to track the users browsing activity. Cookies can be used to remember your preferences, such as your chosen language preference, items in a shopping cart, or if certain settings are turned on. Another popular use of cookies is for logging into websites. When the user visits a websites login page, the web server typically sends the client a cookie containing a unique session identifier. When the user successfully logs in, the server remembers that that particular session identifier has been authenticated and grants the user access to its services.

Cookies are arbitrary pieces of data, usually chosen and first sent by the web server, and stored on the client computer by the web browser. The browser then sends them back to the server with every request, introducing states (memory of previous events) into otherwise stateless HTTP transactions. Without cookies, each retrieval of a web page or component of a web page would be an isolated event, largely unrelated to all other page views made by the user on the website.

Cookies can also be a treasure trove of private information and a serious vulnerability to your privacy. However, most browsers allow you to manage how cookies are set and used as you’re browsing, and to clear cookies and browsing data.