Cookie

cookie, file or part of a file saved to a Web user’s hard disk by a Web site. Cookies are used to store registration data, to make it possible to customize information for visitors to a Web site, to target online advertising, and to keep track of the products a user wishes to order online.

Early browsers often enabled cookies to track which Web sites a user had visited and to retrieve data from other parts of the user’s hard disk. As browser technology became more sophisticated and privacy concerns became more widespread, legitimate Web developers moved away from such practices. Increased attention was paid to the distinction between first-party cookies (those used by the site being visited to facilitate browsing) and third-party cookies (those used by outside domains, often advertisers, to track and monetize browsing on the host site). Anti-malware software often blocked third-party cookies and some browsers rejected them by default.

Lawmakers sought to preserve users’ anonymity and to ensure transparency with measures such as a 2011 European Union directive that required Web sites to disclose their cookie policies and to receive advance consent from users. Such legislation commonly met with widespread compliance but minimal enforcement. As the majority of Internet traffic shifted from desktop Web browsers to mobile browsers and stand-alone applications, the role of cookies changed. Existing cookies were largely incompatible with some mobile browsers, and many popular mobile applications “sandboxed” the cookie data that they collected—that is, information collected within one program was not shared with other programs on the same device.