Employees have stolen more than $200 million from the nation's financial institutions in the past 13 years, with the need to feed a gambling addiction the motivation for more than half the 123 people caught.

A new report, Employee Fraud in Australian Financial Institutions, has found 120 cases of fraud by workers nationwide since January 2000, of which 69 instances involved the big four banks - the National Australia Bank, Commonwealth, Westpac and ANZ - as the victims.

Five of the total cases involved at least $10 million being stolen, the largest amount being $45.3 million taken by a female financial sector employee in NSW. The most common type of fraud committed was when employees stole funds from customers' bank accounts and term deposits.

''When they are stealing from the clients, they are either just taking money out of their bank accounts or raiding their term deposits and putting into their own accounts,'' said report's author, Brett Warfield, from the forensic accounting firm Warfield & Associates.

''Or, they are going in and creating fake loans in customer's names or using fictitious names.''