The BBC reports that computer viruses are the single biggest cause of security problems for UK businesses.
Asurvey by the Department of Trade and Industry found almost 50% of the biggest security breaches suffered by ompanies in the last two years were due to infection by malicious programs.
In some cases viruses crippled key systems such as e-mail for more than a day while companies cleaned up.
The good news revealed by the survey was that the number of firms caught out by viruses had dropped by almost one-third since the last time the study was done in 2004.
Past viruses were designed to cause large amounts of indiscriminate damage typically by taking down targets' networks but today's viruses have become more insidious.
However, almost 25% of those surveyed said they had no defences in place to protect them against spyware. As a result one in seven of the most serious incidents were caused by machines infected with spyware.
The full results of the survey will be released at the InfoSecurity Europe show to help at Olympia in London from 25-27 April.