Large-scale fraud committed against banks rose sharply in the first half of the year.
KPMG's Forensic Fraud Barometer, which looks at data from court cases, revaled more than £630m of alleged fraud in the past six months.
Some £350m was against the financial sector, the highest figure recorded by the barometer in its 20-year history. The sum dwarfed the previous highest figure of £200m, which covered the whole of 1998.
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The record sum was fuelled in part by an alleged attempt to steal £220m by hacking into Sumitomo Matsui Banking Corporation's systems - a case still before the courts.
KPMG warned that the figure was likely to grow further as the credit crunch continues to bite.
The figures come days after the Association of Payment and Clearing Services reported that losses from online banking fraud had dropped by a third in a year.