Compared with previous estimates, costs associated with cleaning up after a virus or worm attack have increased by more than 400 per cent over the past 12 months, to £122,000, says The Corporate IT Forum, which represents the corporate IT user community.

The Forum surveyed its members, which include more than half of the FTSE 100 and 250 companies, after the MSBlast worm this August. The figure of £122,000 is four times that estimated by the Department of Trade and Industry (DTI) last year.

According to the survey, three out of four IT departments spent around 365 person-hours repairing damage caused by the attack. However, 35 per cent of organisations were hit far worse, with each losing an average of 3,080 person-hours.

David Roberts, chief executive of the Corporate IT Forum, said the costs associated with worm and virus clean-up are much higher than expected, especially for smaller companies that do not have the resources required to implement a strong security policies: "Our research is just the tip of the iceberg. The companies surveyed have better than average security and incident response policies in place. Organisations with relatively poor protection will be being hit even harder as they will suffer more downtime and wider business disruption -- as well as getting more viruses in the first place," he said in a statement.

Munir Kotadia writes for ZDNet UK