They promise high returns and present themselves as genuine investment companies, some people do actually make money out of the majorities misery. Read the links below about their sophisicated way of making money. In the early 90's they actually brought down the Albian government, as many of its citizens had invested and lost their money through such schemes in turn blaming their government for not having protected them. These schemes have become a big business in Kenya due to the thirst and hunger for investment opportunities by kenyans.
However, remember that if a deal is too good think twice.