Cookies are small data items a website stores in your browser to remember state, such as a session ID, language choice, or shopping cart contents. Some cookies last only for one session; others persist so the site can recognize you later. Because cookies often carry authentication tokens, they are a core part of how modern web logins work.
In cyber security, cookies matter because stealing or reusing them can let an attacker impersonate a user without knowing the password. Weakly protected cookies can also support tracking across sites or enable session attacks when browser state is shared too broadly. Defenders reduce risk by using flags such as Secure, HttpOnly, and SameSite, rotating session identifiers, and separating browsing contexts so one account’s state does not leak into another. Browser compartmentalization and containers help limit cookie spillover, but they do not replace strong authentication or careful session handling.