To prevent counterfeiting, these notes had many degrees of protection, their designs were changed every five to six months, and they had expiration dates five or six months after the date of issue. The checks worked until the banking system was upgraded to handle electronic transfers of large amounts of đồng, making most large cash transactions unnecessary
After the revaluation of the Zimbabwean dollar on 1 August 2006, the đồng became the least valued currency unit for months. Around 21 March 2007, the revalued Zimbabwean dollar regained least valued currency status (in terms of black market exchange rate), and on 7 September 2007 in terms of official exchange rate. Since the revaluation of the Zimbabwean dollar on 1 August 2008 the đồng was again the least valued currency unit until 11 September 2008, when the Zimbabwean dollar once again surpassed it and on about 20 October in terms of cash rate. On 17 November 2008, the official rate of the Zimbabwean dollar fell below the đồng.
On 3 February 2009, the đồng had this title again as the Zimbabwean dollar re-denominated, although in March 2009 the title was briefly held by the São Tomé and Príncipe dobra. Since Zimbabwe abandoned its dollar on 12 April 2009, the Vietnamese đồng has been the least valued currency.
In 1946, the Viet Minh government (later to become the government of North Vietnam) introduced its own currency, the đồng, to replace the French Indochinese piastre at par. Two revaluations followed, in 1951 and 1958; the first was at a rate of 100:1, the second at a rate of 1000:1.
Notes dually denominated in piastres and đồng were issued in 1953 for the State of Vietnam, which evolved into South Vietnam in 1954. On September 22, 1975, after the fall of Saigon, the currency in South Vietnam was changed to a “liberation đồng” worth 500 old Southern đồng.