Flash cookie

"Flash cookies" are installed when a computer user activates Flash technology, such as a YouTube video, embedded on a site.

Like other cookies, they serve as a tracking device that allows marketers o identity an individual computer and follow its path on every Web visit. Unlike other cookies, Flash cookies can reinstall cookies that have been removed. 

Also known as a "persistent cookie", Flash cookies make it virtually impossible for users to go online without being tracked and profiled.