The enlargement of the European Union is bringing new challenges for Europe's crime fighters - particularly those charged with tackling the counterfeiting of Europe's new currency.
While the euro is said to be harder to counterfeit than any other currency, police around Europe have seen a huge increase of illegal copying in recent months.
The biggest hauls of fakes have come from south-east Europe and the Baltics.
As 10 new countries join the EU, many will already be looking to the day when they can adopt the single currency.
Police said the quality of the notes was 'not good'
But the more widely it is used, the more attractive the currency becomes to counterfeiters - unless the EU's police forces and judicial authorities can keep ahead of the game.
A flood of fake euros is keeping detectives at police headquarters in Hamburg very busy.
In the anti-counterfeit unit, Jurgen Peter Schmidt and his colleagues don their white gloves and scour a pile of notes.
The cash is passed through a special ultra-violet scanner and under a microscope, as officers look for traces that might betray the counterfeiters and their networks.
It is thought these notes come from Bulgaria and the Baltics.
They are mainly 50 euro and 100 euro bills, the most popular among the forgers.
Chief Detective Inspector Schmidt tells me they've seen a spectacular rise in the number of fakes coming into this North German town.
"I predict that by the end of this year we'll be dealing with twice as many fake notes as last year," he says.
"I think that the larger the eurozone becomes the more likely it is the problem will grow. This used to be a national phenomenon - now it's a problem across Europe."
The euro actually has more security features than any other currency.
Mr Schmidt shows me how to spot a fake from the real thing - a watermark, security thread, hologram and raised printing you can feel with a fingernail.
But he and his officers are frustrated that most people aren't aware of all this and don't bother to look. They believe the counterfeiters are taking advantage of this unfamiliarity with the new currency.
"There's no point in adding more security features if people don't make the effort and can't tell the difference between a real note and a fake," he says. "They have to become more vigilant-otherwise the problem will get worse."
Back in Brussels, we decided to put people's knowledge about the currency to the test ourselves. Armed with a fake 50 euro note, we headed for the flower market in the city's main square.
We asked local people and visitors there if they could identify a forgery.
Apart from the shopkeepers, not one person we spoke to had ever checked the notes in their wallet. Few knew what to look for. Nobody identified our note as a fake.
Even the flower seller was taken in. "It's extraordinary - magnificent ," he said scratching his head.
Luckily the EU isn't leaving it up to the citizens to crack the problem of counterfeiting.
Police co-operation between all EU member states and beyond is clearly going to be the key to cracking this racket.
In the Dutch city of The Hague, senior detectives at Europol are sharing and analysing data about forgeries and criminals.
These joint investigations by the so-called "Eurofighters" are bearing fruit. A recent raid on what they call a "print shop" in Serbia revealed a highly sophisticated counterfeiting operation with thousand of fake euro notes recovered.
The high-tech equipment recovered by local police and the fact that the gang seems to stretch across Europe shows detectives what they are up against.
But if the EU really wants to keep pace with the criminals, the director of Europol Juergen Storbeck told me there must be more support for regional police forces on the ground.
"We cannot expect countries, especially poorer countries in Eastern and Central Europe to undertake all the investigations in order to protect our currency," he says.
"They need support: technical support, human resources and perhaps sometimes even payment."
But it's not necessarily all bad news for the law enforcers, struggling to keep ahead as the EU expands.
More member countries could also mean better police co-operation and tougher common rules to tackle the criminals. That will be critical in if citizens are to have confidence in their fledgling currency.