Cookie stuffing is an affiliate fraudulent practice by which an affiliate drops cookies on a user computer without really sending him onto the partner merchant website which set the cookie. Using an affliate link, a call is made to the merchant servers without the visitor knowledge. The cookie is then dropped and associated with the rogue affiliate ID.
Stuffer affiliates use affiliate programs of big merchants because they hope the web users whose computer has been cookie stuffed will make a purchase on the merchant website within the cookie lifetime.
Cookie stuffing can also be done by buying large volumes of low quality ad impressions to drop cookies.
Many other techniques may be used for cookie stuffing:
iFrame on the affiliate website
images posted on forums or with comments
Some cookie stuffers drop several dozens of cookies on each trapped web user and can affect thousands or more rarely millions of users.
The golden age of cookie stuffing seems to be gone, as merchant and affiliate networks are vigilant about it and adopt detection procedures. However, from time to time, new cookie stuffing schemes are unveiled and publicized.
Cookie stuffing is also called cookie dropping and must not be confused with affiliate parasitism.