Almost half of UK businesses have been affected by computer viruses over the past two years; two-fifths of these were described as having a ‘serious impact’ on business.

A telephone survey of 1,000 companies showed virus infections were more likely to have caused service interruption than other incidents. Usually the disruption was minor, but roughly a quarter of companies questioned who reported a virus as their worst incident had major disruption, with important services such as email down for more than a day.

The Department of Trade and Industry’s survey showed the majority of UK businesses surveyed have a broadband link to the internet (88%) and as a result, the threat from as viruses has never been greater. UK businesses have responded and now almost every company uses anti-virus software. Despite the increased threat, fewer companies had viruses than in the last two surveys. Infection rates have dropped by roughly a third since two years ago.

While 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.

Key findings from survey include:

  • A quarter of UK businesses are not protecting themselves against the threat caused by spyware. As a result roughly one in seven of the worst incidents involving malicious software related to spyware that can download onto a computer when the user visits an unscrupulous website.

  • Two years ago, a small number of viruses dominated, for example Netsky and Bagle/Beagle. In contrast over the last year, no single virus has caused widespread damage. Instead the nature of viruses - and the motivation of their writers - has changed. Some malicious viruses, known as 'bots', take over machines turning them into 'botnets" used for cyber crime and cleaning up the problems can take weeks of effort.

  • Patching discipline has improved: nearly nine in 10 UK businesses (88%) apply new operating system security updates within a week of their release, compared with 79% of businesses in 2004.

  • Companies without anti-virus software did not report many infections. One explanation is that companies that suffer virus infection tend to install anti-virus software afterwards.

  • Virus infections tended to take more effort to resolve than other incidents sometimes taking over 50 days' work to fix.