The scale of the problem was revealed this week by the bureau's assistant director in the cyber division, Gordon Snow, in testimony to a House Financial Services Committee subcommittee.

Smart says business employees are being targeted by phishing e-mails containing infected files or links to suspect Web sites, enabling criminals to install malware on their computers to harvest online banking credentials.

The FBI is looking in to over 400 cases where crooks have used this information to steal money from firms' accounts, involving the attempted theft of over $255 million and the actual loss of around $85 million.

In his statement to the subcommittee, Smart also highlighted the financial risk presented by payment processor breaches, ATM skimming, point-of-sale scams, mobile banking exploitation and unauthorised stock trading.

Smart was joined in giving evidence to the subcommittee by representatives from the US Secret Service and the Department of Homeland Security as law-makers formulate their response to the White House's cyber security plans, outlined in May.

In her statement to the subcommittee, US Secret Service assistant director AT Smith, told members that technological advances and the increasing access to personal information online has led to "a marked increase in the quality, quantity and complexity of cyber crimes targeting private industry and critical infrastructure".

Last year the agency saw the arrest of over 1200 suspects for cyber-crime related violations and the examination of 867 terabytes of data. These investigations involved over $500 million in actual fraud loss and prevented another $7 billion, claims Smith.

Greg Schaffer, acting deputy undersecretary, Department of Homeland Security, told members that the mission to reduce the cyber risks posed to the finance sector systems "is a national endeavor, requiring broad collaboration".