A major loss of information is expected to occur once every five years, according to 59 per cent of businesses.

The Symantec IT risk management report also found that companies are concerned that the widespread use of mobile devices will compound the problem of data loss.

"The growth in mobile and portable devices makes assets much harder to track and greatly increases risk," said Jeremy Ward, service development director at the security software supplier.

Nearly half of the respondents ranked mobile devices as a serious risk, but only one third had the ability to manage those risks.

And the growth of mobile computing has placed a higher importance on the training and awareness of staff.

"More process errors were responsible for actual incidents than technology errors – it seems businesses are not using training schemes properly," said Ward.

The number of companies rating their training and awareness programmes as " more than 75 per cent effective" fell from 50 per cent a year ago to 44 per cent.

The average data loss incident exposes the information of more than 785,000 customers and can seriously damage the reputation of a company, according to the report.

"Because customers withdraw from transaction providers and venues they don’t trust, data leakage constitutes a serious threat not only to consumers, but to electronic commerce and banking," it says.

A survey by the Ponemon Institute last year suggested that 62 per cent of consumers are more upset when information loss is due to negligence rather than theft.

According to the Symantec report, IT professionals agree with their customers: 63 per cent believe a data leak would have serious impact on their business.

Organisations with the fewest data losses are testing their controls once every one to three weeks, while those with the biggest problems check procedures only every six months, according to the report.

The study also examined the impact of IT systems failure.

A 10-day network failure at an oil refinery would have an economic impact of $405m (£226m), $180m (£90m) of which would be absorbed by other companies further down the supply chain, according to research from the University of Virginia.