Local shared object
Local shared objects / LSO's are referred to as Flash cookies. A detailed description may be found on:
Some useful information for the Internet user:
A study showing how local shared objects rewrite deleted browser cookies
Study: Adobe Flash cookies pose vexing privacy questions : http://www.networkworld.com/news/2009/081109-study-adobe-flash-cookies-pose.html
Firefox add-ons: BetterPrivacy : visit | add-on Ghostery : visit | add-on