By Jeremy Scott-Joynt
BBC News Online business reporter
When money can cross borders electronically at the touch of a button, the idea of couriers laden with bundles of cash may seem like an anachronism.
As more transactions are reported, are terrorists switching to cash?
Not so, according to the Group of Seven rich nations.
The G7's finance ministers have set their sights on tightening the restrictions on these cash couriers, who are seen as a key element in the funding of extremist groups who may plan attacks on European and US targets.
Electronic fund transfers may be quick and easy, but they leave a paper trail - a risk which bulk cash smuggling can avoid.
Work to do
The G7 nations are at pains to stress they know other, more well-trodden, elements of the fight against terrorist finance need improvement too.
The IMF and World Bank are only now including anti-money laundering and anti-terror finance regulations in their assessments of the health of a country's economy, building on the work of the international anti-financial crime body, the Financial Action Task Force (FATF).
Charities also need better scrutiny.
Drug money is thought to have underwritten the Madrid bombings
And informal money transfer systems such as hawala need to be made more transparent, rather than stamped out, while access to mainstream financial services needs to be made easier.
The ability to freeze assets also needs to be made quicker and more responsive.
All of which, experts in the field would argue, is fine - so far as it goes.
The problem, they say, is that in certain quarters there remains a misunderstanding of just how the funding of terror works.
One key mistake, current and former investigators in both the US and UK tell BBC News Online, is a confusion between financial crime and terrorist finance.
Not that the two don't overlap.
The bomb attack which hit Madrid on 11 March, killing 191 people, was almost certainly part-funded by the proceeds of smuggling marijuana grown in Morocco's Rif mountains.
The FARC in Colombia rely on cocaine and drug-related protection rackets for their funding.
And for the IRA in Northern Ireland, protection rackets, smuggling - of diesel, drugs or anything else - and other forms of criminality were all justified if it helped underwrite the cause.
That overlap creates an opportunity for investigators, because regardless of whether the proceeds of crime head for criminals' pockets or terrorists' plans, they still need to be laundered back into the mainstream economy.
But in two respects, the linking of money laundering and terrorist finance in the minds of both the public and policy-makers causes concern.
Firstly, much of the funding for terror comes not from illegal sources but from legal ones - diverted charity money, and out of the pockets and bank accounts of supporters, for example.
More importantly, the sums involved are miniscule relative to the huge amount of money washing around the financial system.
The best-documented map of terrorist finance to date remains the 9/11 attacks on the US.
Precious stone smuggling is one means of funding terror
The total cost of an operation involving at least 20 people, some living in the US for most of the two preceding years, and training four of them on commercial-grade flight simulators, was probably less than half a million dollars.
And a careful analysis of evidence - including wire transfers from a range of European sources seen by BBC News Online - suggests that the largest single transaction was less than $5,000.
The Madrid bombings will have cost a fraction of that.
In the UK, meanwhile, a spate of arrests in late March revolved around allegations that the discovery of half a tonne of ammonium nitrate fertiliser in a storage unit in West London could be connected to a possible attack.
The unit's rental would have been well under £200 a month, while the ammonium nitrate appears to have been stolen - and in any case would have cost only a few hundred pounds at retail.
Follow the trail
Certainly, stops at borders and reports from financial institutions can produce the goods for investigators.
But security services and law enforcement are sometimes reluctant to give financial institutions, for instance, too many details of what they should look for.
The concern is that someone in one institution or another could pass the information to the very people targeted, enabling them to change their tactics.
Self-storage is not an expensive business
In reality, money trails are less of a tool for alerting the authorities to potential suspects - and more a way of prosecuting the investigation once the initial suspicion is aroused.
That, investigators say, is where financial enquiries really make a difference: allowing a picture to be built up of what suspects do, who they associate with and where they are going.
Increasingly, templates of how funds can flow to terror groups are being built up to aid investigators in following the money - from charities, from crime, via money transfer, false invoices, cash, or through dealings in jewels and high-value goods.
Flood of alerts
But there still remains the perennial problem of "people power".
Suspicious activity reports - the warnings sent to the authorities by banks and other institutions about deals they fear may be problematic - are key source material.
But in the UK, the US, and elsewhere, they are arriving in floods that threaten to overwhelm the personnel available.
That leaves little time or effort to follow up where necessary, while investigators fear the international co-operation needed to follow the trail is well short of what it should be.
And all the G7 statements in the world will do little to help solve that problem.