Contract for differences are derivative assets that a trader uses to speculate on the movement of underlying assets, like stock. If one believes the underlying asset will rise, the investor will choose a long position. Conversely, investors will chose a short position if they believe the value of the asset will fall.
The primary reasons for the ban are concerns over the lack of transparency and the risks associated with leveraged trading. CFDs are over-the-counter (OTC) products, meaning they are traded directly between parties without going through a regulated exchange.