The number of computer fraud cases has doubled, up from 8% of cases in 2001 to 16% in 2004.

The biggest single cause of IT abuse was workers looking at porn or sending suggestive e-mails.

The watchdog said there was a "culture of complacency", despite improved security arrangements.

Inappropriate e-mails

The report by the Audit Commission is based on an online survey carried out in October and November 2004.

They reported 200 cases of abuse and fraud which took place between 2001 and 2004.

Just under half involved workers looking at pornographic or other inappropriate material online. This is a rise from 31% of incidents in 2001 to 47% in 2004.

These included a case where a worker sent inappropriate e-mails to female members of staff.

In another incident, a family member used the login and password of someone working from home to look at porn websites.

In one high-profile case last year, more than 200 civil servants were disciplined for downloading pornographic images at work.

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Fake invoice

The biggest rise was in the cases of fraud, accounting for 16% of incidents in 2004.

In one incident, an employee manipulated the payment system to create a fake invoice and obtain a cheque for £20,280. In another, a worker tinkered with spreadsheets to steal £22,826 over three years.

The problems could get worse, with technologies such as wireless internet access and handheld computers posing new security headaches.

"The growth in new technology coupled with the greater sophistication of hackers and fraudsters, mean that the risks remain significant," said Steve Bundred, chief executive of the Audit Commission.

"ICT (information and communication technology) security is only as effective as the staff within the organisation, and too often we are finding that staff are unsure of their role.

"If we fail to get this right we risk eroding the confidence of citizens in the electronic systems that underpin public services," he said.