Make sure you have updated the flash plugin and delete the data from your previous settings.Almost all major websites are known to exploit this loophole.The cookies will remain in flash local storage if even the you use another browser.So practically all the online activities of user can be tracked.Please make sure you follow the update from adobe :)
Follow this link:
http://help.adobe.com/en_US/FlashPlayer/LSM/WS6aa5ec234ff3f285139dc56112e3786b68c-7fff.html#WS6aa5ec234ff3f285139dc56112e3786b68c-7ffa