Update: Linden Lab changes its mind and allows third-party exchanges with some conditions. Details here.
The online world SecondLife comes with its own currency, Linden Dollars. A number of virtual currency exchanges make a significant portion of their income buying and selling Linden Dollars. Third party exchanging of Linden Dollars has been happening for years and is an important service particularly to SecondLife players outside the States who otherwise do not have a means of purchasing Linden Dollars.
Last week Linden Lab, the SecondLife operator, changed their terms of service to prohibit third-party trading of Linden Dollars.