On December 5, 2013 Twitter announced a new feature to tailor audience. Twitter tracks the website you visit in your browser using third party ad companies. The ad company would then process the collected data and send it back to Twitter. Twitter uses this data to show the user tailored tweets. Luckily one can opt-out by making a change in Twitter settings.
The technique being used is called retargeting marketing, which means if a user visits a website without buying an item Twitter will follow you even after leaving the website and displays the ads repeatedly. Unfortunately this policy is enabled by default. To disable the so called “Promoted Content” one can do so by un-checking the option from Setting>Security and Privacy option
In addition Twitter uses Tailored suggestion, which appears as suggested people to follow, based on the data sent from the ad companies. To opt out, one can disable the Personalization option from the security and privacy setting.
Reference: http://nakedsecurity.sophos.com/2013/12/11/how-twitter-tracks-the-websites-you-visit-and-how-to-stop-it/