The virus hit small businesses in the UK particularly hard, causing millions of pounds worth of damage and lost orders, the Federation of Small Businesses said.
The failure of BT's broadband internet servers, which were still unavailable or running slowly a week after the virus struck, left many firms stranded without e-mail or web access.
Jo Tucker, managing director of online trade body the Interactive Media in Retail Group, described the effect as horrifying. One firm lost a week's worth of business, she said. Online theatre bookers www.whatsonstage.com said its system had shut down after it received more than 5,000 infected e-mails in 24 hours.
Viruses swarm the internet >>