Organised crime syndicates are flooding Australia with counterfeit $50 banknotes, costing businesses and consumers millions of dollars.
More than 33,000 fake $50 notes were removed from circulation in 2014-15, triple the number detected just two years ago, government figures show.
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In 2013, Victoria Police were already investigating 40 reports of counterfeit money being used in stores from Heidelberg to Epping.
But this likely represents only a fraction of the amount of bogus money flowing through the economy amid a massive spike in the number of counterfeiting operations being uncovered by police.
The once state-of-the-art security measures used in the design of the polymer $50 banknote are now more than 20 years old, making it vulnerable to advances in digital imaging and printing technology.
Counterfeiters are now able to produce large runs of fake bills using equipment readily available to the public that are high-quality enough to fool even the forgery detection systems used at banks.
The Reserve Bank of Australia has declined to comment on whether there are security issues with the current $50 banknote, which was designed in 1995.
"While counterfeiting rates have been rising over the past few years, particularly of the $50 banknote, counterfeiting rates remain fairly low by international standards," a RBA spokeswoman said.
But the problem with the $50 note could be worse than estimated amid an explosion in counterfeiting activity.
In Victoria, counterfeiting-related crimes have risen eight-fold since 2010, with more than 1060 offences recorded in the year to September.
There has also been a big spike in the number of active counterfeiting operations being detected.
About one offence related to manufacturing dodgy bills is being recorded every fortnight, according to Victoria's Crime Statistics Agency.
A police investigation revealed the serial numbers from one batch of fake $50 notes had been used more than 760 times around the country.
"This court sees matters where hundreds of thousands of dollars of extremely good quality notes are often produced," County Court Judge John Smallwood said during a 2015 trial.
The counterfeiting operations can range from a couple allegedly working out of their suburban home to fully fledged organised crime syndicates.
The RBA believes the massive spike in the number of counterfeit bills detected in 2015 may have come from just a "single production source".
Often how much fake cash is seized by police is only a fraction of what may have actually been printed.
In one 2010 raid, NSW Police uncovered enough polymer film to manufacture an estimated $40 million worth of counterfeit $50 notes.
Authorities were unable to determine how much dodgy money was ultimately produced by the operation, which was run from a modest family home in the Sydney suburb of Sylvania Waters.
A RBA counterfeiting expert testified the $32,000 worth of finished $50 notes seized by police were "fairly sophisticated" fakes produced on a commercial grade inkjet printer.
"The quality of the $50 notes tendered in evidence was such that I was unable to tell them apart from real currency," NSW District Court Judge Ross Letherbarrow commented at the 2013 trial.
The vast majority of counterfeiting offences relate to criminals caught holding or trying to spend the dodgy bills – known officially by the quaint term "uttering".
Criminals target cash-dependent businesses like pubs, restaurants and market traders to spend the bills, which aren't often detected until deposited at a bank.
Businesses or individuals who have accidentally accepted the dodgy money are not reimbursed for their losses.
Melbourne's Crown Casino has also been sending warning notices to its croupiers warning them about the growing amount of counterfeits in circulation, a source said.
The dodgy currency is also circulating widely among the criminal underworld, often being found during drug busts.
"The bad $50s are rampant right now," an underworld source said.
In NSW, police say the $50 note is the most widely circulated counterfeit in the state but the full scale of the problem is probably under-reported.
"Throughout 2014 and 2015 we saw an increase in the number of counterfeit banknotes being detected, with reports coming through to us from a variety of retailers, restaurants, pubs, clubs and the casino," Detective Superintendent Arthur Katsogiannis, commander of NSW Police's Fraud & Cybercrime Squad, said.
"While many businesses will report counterfeit banknotes to their bank, it's critical they also report them to police so that we can investigate the matter."
Australia is believed to have one of the "most secure" currencies in the world, according to the RBA.
The RBA said it is currently conducting an "upgrade" of the security features of Australia's currency, which will begin with new $5 and $10 notes issued in 2016 and 2017.
The agency declined to comment on when the $50 would be replaced.
"There are some signs that the counterfeiters are getting a bit better with new and cheaper scanning, printing and image manipulation technology," RBA executive Tony Richards acknowledged in a speech last week.
Nine out of every 10 counterfeits detected are $50 banknotes. However, the RBA estimates only about 55 notes out of every million are counterfeit.