consumers based on various traits such as demographics, psychographics, behavioral variables (such as product purchase history), and firmographic variables or other second-order activities which serve as a proxy for these traits. Opt-out cookies Many of the biggest third-party ad-serving companies offer opt-out cookies to users. Opt-out cookies are cookies created by ad-serving companies to enable the user to block and prevent the advertising network from installing future tracking cookies. Opt-out cookies are server specific, meaning that they only block cookies of a specific ad-serving company and won't block cookies from other companies. To do generalized blocking, the users must manage their cookies via their own browser's cookie settings. Do Not Track HTTP header Do Not Track (DNT) is an HTTP header field that requests that a web application or website to disable its direct or cross-site user tracking of an individual user. The header field name is DNT and it currently accepts three values: 1, when the user does not want to be tracked (opt-out) 0, when the user consents to being tracked (opt-in) Null (no header), when the user does not set a preference DNT is not widely adopted by the industry, and honoring DNT requests is not obligatory. Wi-Fi positioning system Wi-Fi-based positioning systems take advantage of the rapid growth of wireless access points in urban areas and are used by companies like Google, Apple, and Microsoft, to obtain data about their customers' locations, in order to provide a better service. The localization technique is based on measuring the intensity of the received signal and access-point "fingerprinting". However, some users have expressed concern about their privacy being affected by this type of unsolicited positioning system, and have asked for opt-out alternatives. Google suggested the creation of a unified approach for opting-out from taking part in Wi-Fi-based positioning systems. Suggesting the usage of the word "_nomap" (Underscore and nomap) append to a wireless access point's SSID to exclude it from Google's WPS database. Postal service Credit card offers Each year American consumers receive several billion written offers of credit or insurance they did not request. In many cases, the senders have prescreened the recipients for creditworthiness and suitability using consumer credit records in the files of consumer reporting agencies. The Fair Credit Reporting Act (FCRA) permits creditors and insurers to use CRA information as a basis for sending unsolicited firm offers of credit or insurance, also known as prescreened