The feature will let shops share email addresses or identity information from software 'cookies' in Web browsers so that Twitter can be able to target people interested in ads from those businesses.
Twitter's targeting advertisements will be also supported by three online tracking firms: media6degrees (m6d), Chango, and Adara. These companies are tracking cookies that are used to predict interests based on sites users have recently visited, and make shopping predictions or otherwise develop targeting criteria. The ad targeting companies communicate the relevant browser cookie ID to Twitter, which will be used to place each user in a bin to receive advertisements "tailored" for that user.
Twitter is also offering users the choise to opt out the new ad scheme, by unchecking the box next to "Promoted content" in their account settings. Opting out will not remove Twitter's ads altogether, but they will prevent Twitter from collecting external data to modify which ads users receive.
And because Twitter supports Do Not Track (DNT), Twitter will not receive browser-related information from its ad partners for tailoring ads if users have DNT enabled in their browsers (Safari, Internet Explorer 9, Chrome, and Firefox.)