Some countries are accused of not co-operating with the US
In a quiet suburb of Stockholm, a secretive meeting is taking place behind closed doors.
From around the world, government experts have flown in to discuss how to close the loopholes in terrorist funding.
The delegates include security officials, bankers and financial investigators.
One of the key speakers is Juan Zarate, the US Deputy Assistant Secretary for Terrorist Financing.
He told me what they're up against.
"We clearly know that al-Qaeda has used the formal financial system before, and they continue to do so.
"But we also do know that they have used underground financial networks and they have certainly corrupted charities around the world to both raise and move funds".
And here lies the problem - trying to regulate the murkiest corners of the world's financial system.
The US Treasury says more than 170 nations have ordered terrorist assets to be frozen.
Dozens of countries have set up Financial Intelligence Units to share information.
But not everyone agrees on how to implement the new measures, introduced after the attacks of 11 September.
Warning to the reluctant
That task falls largely to Patrick Moulette, the Executive Secretary of the FATF, the Financial Action Task Force.
"We have a duty towards the international community to come up with the right measures and its not always easy to agree with 30 plus countries because the measures are complex".
Those measures include an eight-point action plan drawn up by the FATF.
It requires countries to make financing terrorism a crime, for banks to know exactly who their customers are, and to report suspicious transactions immediately.
Well, that may sound like common sense.
Can a financial clampdown break the back of terrorism?
But according to the FATF President, Claes Norgren, there are a number of countries that are still not cooperating.
"My message to the countries who would not take action in this, is that this is something that is problem to us all and you have to realise that if you don't take action you will suffer too."
Later, some of the world's leading financial "spooks" - the men and women who work fulltime to try and choke off the funding still reaching the militants, relax over Swedish salmon in a restaurant.
I asked the US Treasury's Juan Zarate how much success he thinks they're having.
"We feel like we've been extremely successful.
"We've tightened the net around al-Qaeda, we've cut off channels of funding, we've frozen more than $136m in terrorist related assets, identified and designated over 315 terrorist related individuals and entities, we've clearly deterred terrorist fundraising and funding."
Tracking terror funding through the banking system is one thing. But it can be much harder if it goes underground.
And of course, terrorism can be frighteningly cheap.
Al Qaeda continues to exploit international financial systems
The attacks of 11 September cost a tiny fraction of Osama Bin Laden's wealth.
Even Juan Zarate admits the financial clampdown won't stop the attacks.
"It will be very difficult to ever stop the singular terrorist attack, but what we can hope to do is stop the major attacks, to stop the major movement of funds and cut off the long-term ability of terrorists to attack Western civilisation".
So far, there has not been a repeat of anything on the scale of 9/11. But the al-Qaeda movement is far from bankrupt and its followers do have endless patience.