Hyperinflation effectively wipes out the purchasing power of private and public savings, distorts the economy in favor of the hoarding of real assets, causes the monetary base, whether specie or hard currency, to flee the country, and makes the afflicted area anathema to investment. But one of the most important characteristics of hyperinflation is the accelerating substitution of the inflating money by stable money, gold and silver in former times, but relatively stable foreign currencies after the breakdown of the gold or silver standards (Adolphe Thiers's Thiers' Law). If inflation is high enough all government regulations like heavy penalties and fines often combined with exchange controls cannot prevent this currency substitution. As a consequence the inflating currency is usually heavily undervalued compared to stable foreign money and in terms of purchasing power parity. As a consequence foreigners can live cheaply and buy at cheap prices in the countries hit by high inflation. It follows that governments who do not succeed to engineer in time a successful currency reform have finally to legalize the stable foreign currencies (or formerly gold and silver) which is threatening to fully substitute the inflating money. Otherwise their tax revenues including the inflation tax will approach zero.[15] The last hyperinflation where this process could be observed, took place in Zimbabwe in the first decade of the 21st century. In this case the local money was mainly driven out by the US dollar and the South African rand.