Cookie sharing

Cookies were set up with the intention that each site has its own cookies and that they are only readable by that website. Any one site should not be able to alter or set cookies for another site. However if a website allows a third party to cookie its users (typically by facilitating the delivery of the third party’s cookie through the given website) then that third party can share data with other websites that behave in a similar way. This is the foundation for the data that is gathered by advertising networks that use behavioural advertising. See also: Cookie, Behavioral targeting.