Specialist software has allowed online bank Egg to close the net on the gang behind an Internet credit card scam.
Electronic evidence gathered by Egg during a six-month investigation led to the arrest of three people during raids by the National Crime Squad last week.
Police seized computer equipment, cash, drugs and documentation during the raids, code-named Operation Skoda, in Milton Keynes, Bedfordshire and Buckinghamshire.
Egg discovered the fraud in February when detection software began to pick up inconsistencies in a series of credit card applications made over the Internet.
Bogus applications were detected by Hunter, an off-the-shelf package produced by MCL, which checks the accuracy of entries on application forms, such as employers' names and individuals' dates of birth, against a database.
Falcon, another off-the-shelf software package, enabled Egg to identify suspected fraudsters that managed to evade the Hunter system by gathering evidence of unusual spending patterns
Egg also developed its own software to identify common threads among the fraudulent applications, such as multiple cards ordered from the same PC, enabling police to home in on the gang.
Despite its recent success, Egg said it would continue to improve its fraud detection software.
"We are achieving very good results with our fraud detection. But we will continue to enhance them because the fraudsters change their methods. We need to keep ahead of them," said Gary Clifton-Marshall, operations director of Egg.
The National Crime Squad believes other Internet banks may have been victims of similar fraud.
"This has been a very complex investigation involving organised criminals who we believe have been using the Internet as a medium for committing serious crime and for targeting the relatively new Internet banks," said Detective Sergeant Mick Randall.
The three people arrested have been released on bail without charge, pending further enquiries.