Berkshire and Wiltshire Business Link found that more than half of all UK businesses were subject to an attack during 2003 despite 90 per cent using anti-virus software.

Its research also showed that less than 60 per cent of companies updated their anti-virus software at regular intervals.

In the first three months of 2004 viruses including MyDoom, Netsky and Bagle have infected more computer systems than ever before, costing businesses time, money and inconvenience.

The result of virus attacks range from minor interruptions to business through to major disruption, although the outcomes can be far worse if any of the viruses are programmed to delete files, corrupt data or wipe hard drives.

The damage, and time taken to delete spurious e-mails generated by these viruses, often results in numerous financial costs to businesses including the potential loss of business and the time and cost of re-instating computer systems.

Andrew Poulton, e-business adviser of the ICT team for Berkshire and Wiltshire Business Link, said: “The key to minimising the risk of infection is to have a multi-layered defence which starts with educating users.

“Most of the viruses use social engineering in an attempt to tempt the user to open the file that arrives by e-mail.

“Computer users need to consider any e-mail that arrives with an unexpected attachment as a risk and delete accordingly.”

The next layer is to ensure software is installed and regularly updated to combat any viruses.

Systems should be updated on a weekly basis and firewall technologies should also be deployed to prevent unauthorised access.

Mr Poulton added: “The other crucial area where businesses can take measures to protect themselves is to ensure that all their business critical data is regularly backed-up, and where possible, these back-ups are stored off-site.

“Periodically the company should also ensure they can restore their data back on their computers.

“If all these measures are enforced the company will face a much lower risk of infection.”

For further information and advice on computer viruses contact Berkshire and Wiltshire Business Link on (08456) 004 141.