I reproduce the wikipedia information

Money laundering

Money laundering is the process of concealing the source of money obtained by illicit means. The methods by which money may be laundered are varied and can range in sophistication. Many regulatory and governmental authorities quote estimates each year for the amount of money laundered, either worldwide or within their national economy. In 1996, the International Monetary Fund estimated that two to five percent of the worldwide global economy involved laundered money. However, the Financial Action Task Force on Money Laundering (FATF), an intergovernmental body set up to combat money laundering, stated that "overall it is absolutely impossible to produce a reliable estimate of the amount of money laundered and therefore the FATF does not publish any figures in this regard".^[1] Academic commentators have likewise been unable to estimate the volume of money with any degree of assurance.^[2]

Regardless of the difficulty in measurement, the amount of money laundered each year is in the billions (US dollars) and poses a significant policy concern for governments.^[2] As a result, governments and international bodies have undertaken efforts to deter, prevent and apprehend money launderers. Financial institutions have likewise undertaken efforts to prevent and detect transactions involving dirty money, both as a result of government requirements and to avoid the reputational risk involved.