Infection by viruses was the biggest single cause of the worst security incidents for UK companies in the past two years, accounting for roughly half of them, a new survey shows

Two-fifths of these were described as having a serious impact on the business, according to findings from the 2006 UK Department of Trade and Industry's biennial Information Security Breaches Survey, conducted by a consortium led by PricewaterhouseCoopers LLP. The full results will be launched at Infosecurity Europe in London, 25-27 April.

The survey showed that virus infections were more likely to have caused service interruption than other incidents. Usually the disruption was minor, but roughly a quarter of companies who reported a virus as their worst incident had major disruption, with important services, such as e-mail, down for more than a day.

Although infection rates have dropped by roughly a third since two years ago, and the number of companies infected has fallen since 2004, the average number of infections suffered by those affected has risen to roughly one a day. Several businesses reported hundreds of infections a day.

The factsheet 'Viruses and malicious spyware' can be downloaded from