Cyber crime is rising in the US, but two thirds of all security breaches are still not being reported to the relevant authorities, according to the FBI.

The Bureau's seventh annual report, written in conjunction with the Computer Security Institute (CSI), warned that US companies are losing most money through the loss of proprietary information.

These losses cost US businesses $170m last year, with financial fraud amounting to $115m, the Computer Crime and Security survey found.

Although 90 per cent of companies interviewed admitted that they had identified security breaches in the past 12 months, only 34 per cent reported the intrusion to law enforcement authorities.

Some 78 per cent said they had detected internet abuse by an employee.

But the breaches are occurring despite attempts by respondents to safeguard their systems. A total of 90 per cent use antivirus software and 89 per cent use firewalls.

"There is much more illegal and unauthorised activity going on in cyberspace than corporations admit to clients, stockholders and business partners," said CSI director Patrice Rapalus.