A Ponzi scheme is a fraudulent investment operation that pays returns to separate investors from their own money or money paid by subsequent investors, rather than from any actual profit earned. The Ponzi scheme usually entices new investors by offering returns other investments cannot guarantee, in the form of short-term returns that are either abnormally high or unusually consistent. The perpetuation of the returns that a Ponzi scheme advertises and pays requires an ever-increasing flow of money from investors to keep the scheme going.
The system is destined to collapse because the earnings, if any, are less than the payments to investors. Usually, the scheme is interrupted by legal authorities before it collapses because a Ponzi scheme is suspected or because the promoter is selling unregistered securities. As more investors become involved, the likelihood of the scheme coming to the attention of authorities increases. While the system eventually will collapse under its own weight.
The scheme is named after Charles Ponzi, who became notorious for using the technique in early 1920. He had emigrated from Italy to the United States in 1903. Ponzi did not invent the scheme (Charles Dickens' 1857 novel Little Dorrit described such a scheme decades before Ponzi was born, for example), but his operation took in so much money that it was the first to become known throughout the United States. His original scheme was in theory based on arbitraging international reply coupons for postage stamps, but soon diverted investors' money to support payments to earlier investors and Ponzi's personal wealth.
Ponzi scheme and PTC
Most of PTC website and especially bux type website use Ponzi scheme. There is not enough real advertisers there so they ask for new deposits from their members (referral and upgrades purchases) to be able to cover expenses of the website. After some time the income from investors becomes lower than the amount of money the website owes it's members and the results of it are payment delays or the closure of website (scam)