BBC Frontline Scotland
This has been, even by Frontline standards, a lengthy and complex investigation. Mind you, at the heart if it is a huge international fraud and you don't crack that kind of crime overnight.
Billions of pounds are being stolen by organised gangs who get access to our bank and credit card accounts.
We wanted to find out how they did it, test the security measures that are in place to stop them and, most difficult of all, track down the masterminds behind this lucrative crime.
We started by talking to victims, and there are plenty of them out there.
One man told us he was puzzled when his credit card account suddenly started having money paid into it. At one point he was £3,600 in credit.
What he didn't know was that criminals had hacked into his account and were using it to launder stolen cash. Then all the money, including his, was cleared out.
He had been the victim of telephony fraud, and as the name suggests, the telephone is at the centre of this crime.
Someone pretending to be from his bank had phoned and fooled him into giving out vital information. Then the false caller took on his identity, called his bank and got more personal details.
The criminals assembled a complete dossier of confidential financial information. Then bingo, they were into his account.
Take this example, and multiply it by tens of thousands, and the rewards begin to add up.
Fraud crime costs £14bn per year in the UK
Telephone fraud worth between £1bn - £3bn per year
Costs each person £300 per year in bank charges
But where did the criminals get the initial information that allowed them to start the whole process?
Well, we knew call centres - the type we all phone on a regular basis - had been targeted in the past . Rogue workers can steal confidential details and sell them on or in some cases the criminals themselves manage to get jobs.
To check this out we had an undercover journalist apply for a job at one of Scotland's biggest call centre operations - RHL, which is branded as Response.
She was successful. During her training the issue of security was hammered home loud and clear. But once she started the job proper there were two troubling lapses.
She was able to write down customers' account details on bits of paper, put them in her handbag and remove them from the building.
Priceless information in the hands of the wrong person.
Employee vetting is also very important when confidential information is being handled on a daily basis. But our investigator's references were never checked out by the company.
We obviously wanted to get RHL's reaction to all this. But when we approached the company with our findings RHL's response was to go to court in a bid to stop our programme being broadcast.
That failed and a judge ruled in favour of the BBC.
RHL then told us it took our findings very seriously and were always looking at ways of improving procedures.
Convicted killer Imran Shahid runs the fraud gang
We knew this type of crime was going on across the UK. Now we wanted to find out just who was making money out of it.
Our sources led us to believe that one of the biggest criminal gangs involved - with operations that spanned the globe - was based right on our doorstep here in Scotland, on Glasgow's south side.
And we had uncovered a remarkable link with that gang.
Remember the fraud victim I told you about earlier? Well, Frontline came across his name and financial details - along with dozens of others -written in a ledger found in a flat in the Pakistan city of Lahore.
The flat was being used as a hideout by one of the men wanted for the murder of Glasgow schoolboy Kriss Donald. Three men were later extradited back to Scotland and are now serving life sentences.
We managed to track down a former gang member who confirmed the killers were the masterminds behind a criminal enterprise that was stealing financial details, accessing accounts and getting away with millions of pounds.
Despite the men now being behind bars, the story doesn't end there. Our insider warned that other criminals have stepped into their shoes and this multi-million pound fraud is still going on.
To find out more, watch Frontline:The Billion Pound Bank Robbery on BBC One Scotland at 1900 BST on Wednesday, 30 May (Digital Satellite channel 971).