HTTP cookie http://en.wikipedia.org/wiki/HTTP_cookie
Are cookies really spyware and are they dangerous? http://superantispyware.com/supportfaqdisplay.html?faq=26
https://www.google.no/search?q=how+do+i+block+third+party+cookies&oq=how+do+i+block+third+party+cookies&aqs=chrome.0.69i57j0l3j69i62.10242j0&sourceid=chrome&ie=UTF-8#bav=on.2,or.r_qf.&fp=1b41445e7dadd3b1&q=how+to+block+third+party+cookies