Australia's counterfeit banknote rate rose sharply during the 2010/11 financial year, reaching almost double the normal rate.The Reserve Bank says the long-term average is for eight counterfeit banknotes per million in the system. But yesterday the RBA reported that the rate jumped to 16 parts per million during the last financial year.The RBA said this was a temporary increase, which has fallen back following a number of arrests.Australian counterfeiting rates are low by world standards. Rates of 50 to 100 parts per million are common in other countries.Among local counterfeiters, the preferred denomination is the $50 banknote. Eighty per cent of all counterfeits detected are $50 notes.The reason for this is that the $50 note is the most widely used banknote, representing more than half of the 1.1 billion banknotes in circulation.